P0590 Multifunction Input B Circuit of the Cruise Control Stuck

What Does It Mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles. This may include, but is not limited to, vehicles from Mazda, Alfa Romeo, Ford, Land Rover, Jeep, Dodge, Chrysler, Chevy, Nissan, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

Cruise control was developed for our comfort. Its sole purpose is to manually maintain the vehicle speed set by the operator (via steering wheel buttons, the multifunction switch (i.e., turn signals, cruise control, wipers, etc.) mounted on the steering column, etc.)

Meanwhile, the operator no longer has to control the accelerator pedal, and if the vehicle is equipped with an automatic transmission (A/T), it can also control and adjust shift points based on real-time driving condition requirements.

Generally speaking here, this code would lead me to believe we are talking about the multifunction switch on your steering column. That said, location possibilities vary significantly from one manufacturer to another, so research accordingly. The cruise control button would be a good place to start narrowing down locations. This code refers to a specific input circuit in the cruise control system. To determine which wire/circuit to focus on, refer to the service manual; the letters in the codes can and will be your best reference regarding the identification of the wire/circuit you are trying to diagnose/test.

In case of a fault in the cruise control multifunction input “B” circuit, the Engine Control Module (ECM) proactively illuminates the instrument cluster with P0590 and related codes (P0589, P0590, P0591, P0592, and P0593).

Regarding the letter “B,” it could be to distinguish a connector, a wire, a circuit group, etc. That said, manufacturer specifications are the best resource you can have for this.

P0590 is set by the ECM when the cruise control multifunction “B” input is electronically (or possibly mechanically) “stuck.”

A cruise control stalk:


P0590 Cruise Control Stalk
How Severe Is This DTC?

Low severity for almost all cruise control faults; that said, there are many exceptions. For the most part, however, this fault should not be a source of serious concern. That said, when it comes to electrical issues, they generally worsen over time. Most of the time, this fault will be moderately affordable to fix.

Obviously, this is very subjective, so be sure to shop around for the best prices and get multiple quotes/diagnostic strategies; who knows, work orders alone might help you determine what you’re dealing with. Always stay on top of general vehicle maintenance.
What Are Some of the Symptoms of the Code?

Symptoms of a P0590 trouble code may include:

Abnormal vehicle speeds with cruise control activated
Inoperative cruise control
Cruise control indicator light is on regardless of switch position
Unable to set cruise control to the desired speed

What Are Some of the Common Causes of the Code?

Causes

of this P0590 code may include:

Faulty multifunction/cruise control switch (i.e., stuck, broken, missing, etc.)
Wiring issue (e.g., rubbing on steering column/dashboard parts, water intrusion, corrosion, etc.)
Connector malfunction (e.g., corroded pins, broken plastic tabs, swollen connector body, etc.)
Liquids/dirt/grime in the cruise control button/switch causing abnormal mechanical operation
ECM problem (e.g., water intrusion into the computer body, internal short circuit, internal overheating, etc.)

What Are the Troubleshooting Steps for P0590?
Basic Step #1

Once your vehicle’s multifunction/cruise control switch is located, visually inspect it for any type of contamination. It is very easy for plastic buttons/switches to become dirty/greasy/sticky, making them faulty and/or operating abnormally. Ensure the mechanical operation of the switch is smooth and fluid. Any issues here should be addressed immediately. If your specific scan tool/OBD reader has the capabilities, feel free to observe the electronic operation of the switch via DATA STREAM (the mode name varies here between readers, but the important thing is to find a mode to observe real-time data).

TIP: Be careful not to spray cleaning solutions directly onto the button. Lightly dampen a clean cloth with water, soap and water, dashboard cleaner, etc., and carefully remove debris from the switch crevices. A compressed air gun will help remove debris without making the situation worse.
Basic Step #2

To access the connectors and harnesses involved in the cruise control/multifunction switch input circuit, you may need to remove some dashboard plastics/covers. Be gentle when working with plastic. Comfortable ambient temperatures always contribute to the ease of disassembling/assembling dashboard/interior plastics.

If you can easily access the connector, you may be able to apply specific troubleshooting steps provided by your service manual. Switch testing will most likely involve recording electrical values using your multimeter. This may include using the switch during recording and/or static tests. Refer to the specific make and model service manual for the “diagnostic diagram.”
Basic Step #3

A problem within the ECM is, most of the time, the last resort in diagnosis. Since this might be one of the most expensive electronic repairs you could perform on your vehicle, leave this to the professionals.

P0591 Multifunction Input B Circuit Range/Performance of Cruise Control

What does it mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles. This may include, but is not limited to, vehicles from Mazda, Alfa Romeo, Ford, Land Rover, Jeep, Dodge, Chrysler, Chevy, Nissan, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

Cruise control was developed for our comfort. Its sole purpose is to manually maintain the vehicle speed set by the operator (via steering wheel buttons, the multifunction switch (i.e., turn signals, cruise control, windshield wipers, etc.) mounted on the steering column, etc.)

Meanwhile, the operator no longer has to control the accelerator pedal, and if the vehicle is equipped with an automatic transmission (A/T), it can also control and adjust shift points based on real-time driving condition requirements.

Generally speaking here, this code would lead me to believe we are talking about the multifunction switch on your steering column. That said, location possibilities vary significantly from one manufacturer to another, so research accordingly. The cruise control button would be a good place to start narrowing down locations. This code refers to a specific input circuit in the cruise control system. To determine which wire/circuit to focus on, refer to the service manual; the letters in the codes can be and will be your best reference regarding identifying the wire/circuit you are trying to diagnose/test.

If a fault occurs in the cruise control multifunction input circuit “B”, the Engine Control Module (ECM) proactively illuminates the instrument cluster with P0591 and related codes (P0589, P0590, P0591, P0592, and P0593).

Regarding the letter “B”, it could be to distinguish a connector, a wire, a circuit group, etc. That said, manufacturer specifications are the best resource you can have for this.

The P0591 fault code is set by the ECM when the values from the cruise control multifunction input circuit “B” are out of range or operating abnormally.

A cruise control actuator:
P0591 Cruise Control Actuator
How severe is this DTC?

Low severity for almost all cruise control faults, that said, there are many exceptions. For the most part, however, this fault should not be a source of serious concern. That said, when it comes to electrical issues, they generally worsen over time. Most of the time, this fault will be moderately affordable to fix.

Obviously, this is very subjective, so be sure to shop around for the best prices and get multiple quotes/diagnostic strategies; who knows, work orders alone might help you identify what you’re dealing with. Always stay on top of general vehicle maintenance.
What are some of the symptoms of the code?

Symptoms of a P0591 trouble code may include:

Abnormal vehicle speeds with cruise control activated
Inoperative cruise control
Cruise control indicator light is on regardless of the switch position
Unable to set the cruise control to the desired speed

What are some of the common causes of the code?

Causes

of this P0591 code may include:

Faulty multifunction/cruise control switch (i.e., stuck, broken, missing, etc.)
Wiring issue (e.g., rubbing on steering column/dashboard parts, water intrusion, corrosion, etc.)
Connector malfunction (e.g., corroded pins, broken plastic tabs, swollen connector body, etc.)
Liquids/dirt/grime in the cruise control button/switch causing abnormal mechanical operation
ECM problem (e.g., water intrusion into the computer body, internal short circuit, internal overheating, etc.)

What are the troubleshooting steps for P0591?
Basic Step #1

Once your vehicle’s multifunction/cruise control switch is located, visually inspect it for any type of contamination. It is very easy for plastic buttons/switches to become dirty/greasy/sticky, leading to their malfunction and/or abnormal operation. Ensure the mechanical operation of the switch is smooth and fluid. Any issues here must be addressed immediately. If your specific scan tool/OBD reader has the capabilities, feel free to observe the electronic operation of the switch via DATA STREAM (the mode name varies here between readers, but the important thing is to find a mode to observe real-time data).

TIP: Be careful not to spray cleaning solutions directly onto the button. Lightly dampen a clean cloth with water, soap and water, dashboard cleaner, etc., and carefully remove debris from the switch’s crevices. A compressed air gun will help remove debris without making the situation worse.
Basic Step #2

To access the connectors and harnesses involved in the cruise control/multifunction switch input circuit, you may need to remove some dashboard plastics/covers. Be gentle when working with plastic. Comfortable ambient temperatures always contribute to the ease of disassembling/assembling the dashboard/interior plastics.

If you can easily access the connector, you might be able to apply specific troubleshooting steps provided by your Al. Switch testing will most likely involve recording electrical values using your multimeter. This may include using the switch while recording and/or static tests. Refer to the specific make and model service manual for a “diagnostic flowchart.”
Basic Step #3

A problem within the ECM is, most of the time, the last resort in diagnosis. Since this might be one of the most expensive electronic repairs you could perform on your vehicle, leave this to the professionals.

P0592 Multifunction Input Circuit B of Low Cruise Control

What Does It Mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles. This may include, but is not limited to, vehicles from Mazda, Alfa Romeo, Ford, Land Rover, Jeep, Dodge, Chrysler, Chevy, Nissan, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

Cruise control was developed for our comfort. Its sole purpose is to manually maintain the vehicle speed set by the operator (via steering wheel buttons, the multifunction switch (i.e., turn signals, cruise control, wipers, etc.) mounted on the steering column, etc.)

Meanwhile, the operator no longer has to control the accelerator pedal, and if the vehicle is equipped with an automatic transmission (A/T), it can also control and adjust shift points based on real-time driving condition requirements.

Generally speaking here, this code would lead me to believe we are talking about the multifunction switch on your steering column. That said, location possibilities vary significantly from one manufacturer to another, so research accordingly. The cruise control button would be a good place to start narrowing down locations. This code refers to a specific input circuit in the cruise control system. To determine which wire/circuit to focus on, refer to the service manual; the letters in the codes can and will be your best reference regarding the identification of the wire/circuit you are trying to diagnose/test.

When a fault occurs in the cruise control multifunction input circuit “B”, the Engine Control Module (ECM) proactively illuminates the instrument cluster with P0592 and related codes (P0589, P0590, P0591, P0592, and P0593).

Regarding the letter “B”, it could be to distinguish a connector, a wire, a circuit group, etc. That said, manufacturer specifications are the best resource you can have for this.

The P0592 code is set by the ECM when the electrical value of the cruise control multifunction input circuit “B” is unexpected.

A cruise control stalk:


P0592 Cruise Control Stalk
How Severe Is This DTC?

Low severity for almost all cruise control faults, that said, there are many exceptions. For the most part, however, this fault should not be a source of serious concern. That said, when it comes to electrical issues, they generally worsen over time. Most of the time, this fault will be moderately affordable to fix.

Obviously, this is very subjective, so be sure to shop around for the best prices and get multiple quotes/diagnostic strategies; who knows, work orders alone might help you identify what you’re dealing with. Always stay on top of general vehicle maintenance.
What Are Some of the Symptoms of the Code?

Symptoms of a P0592 trouble code may include:

Abnormal vehicle speeds with cruise control activated
Inoperative cruise control
Cruise control indicator light is on regardless of switch position
Unable to set cruise control to the desired speed

What Are Some Common Causes of the Code?

Causes

of this P0592 code may include:

Faulty multifunction/cruise control switch (i.e., stuck, broken, missing, etc.)
Wiring issue (e.g., rubbing on steering column/dashboard parts, water intrusion, corrosion, etc.)
Connector malfunction (e.g., corroded pins, broken plastic tabs, swollen connector body, etc.)
Liquids/dirt/grime in the cruise control button/switch causing abnormal mechanical operation
ECM problem (e.g., water intrusion into the computer body, internal short circuit, internal overheating, etc.)

What Are the P0592 Troubleshooting Steps?
Basic Step #1

Once your vehicle’s multifunction/cruise control switch is located, visually inspect it for any type of contamination. It is very easy for plastic buttons/switches to become dirty/greasy/sticky, leading to their malfunction and/or abnormal operation. Ensure the mechanical operation of the switch is smooth and fluid. Any issues here should be addressed immediately. If your particular scan tool/OBD reader has the capabilities, feel free to observe the electronic operation of the switch via DATA STREAM (the mode name varies here between readers, but the important thing is to find a mode to observe real-time data).

TIP: Be careful not to spray cleaning solutions directly onto the button. Lightly dampen a clean cloth with water, soap and water, dashboard cleaner, etc., and carefully remove debris from the switch’s crevices. A compressed air gun will help remove debris without making the situation worse.
Basic Step #2

To access the connectors and harnesses involved in the cruise control/multifunction switch input circuit, you may need to remove some dashboard plastics/covers. Be gentle when working with plastic. Comfortable ambient temperatures always contribute to the ease of disassembling/assembling dashboard/interior plastics.

If you can easily access the connector, you might be able to apply specific troubleshooting steps provided by your service manual. Switch testing will most likely involve recording electrical values using your multimeter. This may include using the switch during recording and/or static tests. Refer to the specific make and model service manual for the “diagnostic diagram.”
Basic Step #3

A problem within the ECM is, most of the time, the last resort in diagnosis. Since this might be one of the most expensive electronic repairs you could perform on your vehicle, leave this to the professionals.

P0593 High Speed Cruise Control Multifunction Input B Circuit

What Does It Mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles. This may include, but is not limited to, vehicles from Mazda, Alfa Romeo, Ford, Land Rover, Jeep, Dodge, Chrysler, Chevy, Nissan, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

Cruise control was developed for our comfort. Its sole purpose is to manually maintain the vehicle speed set by the operator (via steering wheel buttons, the multifunction switch (i.e., turn signals, cruise control, wipers, etc.) mounted on the steering column, etc.)

Meanwhile, the operator no longer needs to control the accelerator pedal, and if the vehicle is equipped with an automatic transmission (A/T), it can also control and adjust shift points based on real-time driving condition requirements.

Generally speaking here, this code would lead me to believe we are talking about the multifunction switch on your steering column. That said, location possibilities vary significantly from one manufacturer to another, so research accordingly. The cruise control button would be a good place to start narrowing down locations. This code refers to a specific input circuit in the cruise control system. To determine which wire/circuit to focus on, refer to the service manual; the letters in the codes can and will be your best reference regarding identifying the wire/circuit you are trying to diagnose/test.

When a failure occurs in the cruise control multifunction input circuit “B,” the Engine Control Module (ECM) proactively illuminates the instrument cluster with P0593 and related codes (P0589, P0590, P0591, P0592, and P0593).

Regarding the letter “B,” it could be to distinguish a connector, wire, circuit group, etc. That said, manufacturer specifications are the best resource you can have for this.

The P0593 code is set by the ECM when a high electrical value is detected in the cruise control multifunction input circuit “B.”

A Cruise Control Stalk:


P0593 Cruise Control Stalk
How Severe Is This DTC?

Low severity for almost all cruise control faults; that said, there are many exceptions. For the most part, however, this fault should not be a source of serious concern. That said, when it comes to electrical issues, they generally worsen over time. Most of the time, this fault will be moderately affordable to fix.

Obviously, this is very subjective, so be sure to shop around for the best prices and get multiple quotes/diagnostic strategies; who knows, work orders alone might help you determine what you’re dealing with. Always stay on top of general vehicle maintenance.
What Are Some of the Symptoms of the Code?

Symptoms of a P0593 trouble code may include:

Abnormal vehicle speeds with cruise control activated
Inoperative cruise control
Cruise control indicator light on regardless of switch position
Unable to set cruise control to the desired speed

What Are Some of the Common Causes of the Code?

Causes

of this P0593 code may include:

Faulty multifunction/cruise control switch (i.e., stuck, broken, missing, etc.)
Wiring issue (e.g., rubbing on steering column/dashboard parts, water intrusion, corrosion, etc.)
Connector malfunction (e.g., corroded pins, broken plastic tabs, swollen connector body, etc.)
Liquids/dirt/grime in the cruise control button/switch causing abnormal mechanical operation
ECM problem (e.g., water intrusion into the computer body, internal short circuit, internal overheating, etc.)

What Are the P0593 Troubleshooting Steps?
Basic Step #1

Once your vehicle’s multifunction/cruise control switch is located, visually inspect it for any type of contamination. Plastic buttons/switches can easily get dirty/greasy/sticky, making them faulty and/or operate abnormally. Ensure the mechanical operation of the switch is smooth and fluid. Any issues here should be addressed immediately. If your specific scan tool/OBD reader has the capabilities, feel free to observe the electronic operation of the switch via DATA STREAM (the mode name varies between readers, but the important thing is to find a mode to observe real-time data).

TIP: Be careful not to spray cleaning solutions directly onto the button. Lightly dampen a clean cloth with water, soap and water, dashboard cleaner, etc., and carefully remove debris from the switch’s crevices. A compressed air gun will help remove debris without making the situation worse.
Basic Step #2

To access the connectors and harnesses involved in the cruise control/multifunction switch input circuit, you may need to remove some dashboard plastics/covers. Be gentle when working with plastic. Comfortable ambient temperatures always contribute to the ease of disassembling/assembling dashboard/interior plastics.

If you can easily access the connector, you might be able to apply specific troubleshooting steps provided by your service manual. Switch tests will most likely involve recording electrical values using your multimeter. This may include using the switch during recording and/or static tests. Refer to the specific make and model service manual for the “diagnostic diagram.”
Basic Step #3

A problem within the ECM is, most of the time, the last resort in diagnosis. Since this might be one of the most expensive electronic repairs you could perform on your vehicle, leave this to the professionals.

P0594 Cruise Control Servo Control Circuit / Open

What Does It Mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles with cruise control. Vehicle makes may include, but are not limited to, Dodge, Chrysler, Ram, Jeep, Hyundai, BMW, Vauxhall, Mini, Chevrolet, etc.

There are many benefits that come with the cruise control function. On long trips, there’s no need to constantly monitor and adjust speeds based on traffic and traffic laws. You press a button or two, and a combination of sensors, solenoids, modules, etc., ensures the vehicle keeps moving at the specified speed until you, or possibly external influences, deactivate or adjust the speed accordingly. Not to mention, the vehicle will have a good idea of how to maintain fuel economy at a good level throughout the journey, as when we drive, we don’t necessarily take everything into account to reduce costs.

Fortunately for us, the ECM (Engine Control Module) is responsible for the smooth but effective operation of the cruise control. The proper functioning of the systems relies on many sensors, switches, modules, VSS, etc. One of them being the cruise control servo. Most of the time, these are responsible for throttle control when you set and/or adjust the cruise control. By controlling the throttle and adjusting accordingly, with this servo, the ECM can adjust the speed easily and effectively. Many times, these servos are mechanically controlled via vacuum lines and throttle cables. The servo’s vacuum is controlled by solenoids which are, in turn, controlled by the ECM, which can interpret all other values before specifying throttle position, speed, etc. This fault refers to the circuit involved; refer to the service manual to determine exactly which physical circuit you are working on/diagnosing.

The P0594 Cruise Control Servo Circuit/Open and related codes (P0525, P0595, and P0596) are set when the ECM monitors a malfunction in the cruise control servo circuit. In the case of P0594 specifically, it is set when a general failure or an open electrical condition is detected in said circuit.

Example of a Cruise Control Servo:


P0594 Cruise Control Servo
How Severe Is This DTC?

I will set the severity of this code to medium. Regarding most OBD2 cruise control error codes, they are quite minor. That being said, in this case, because the cruise control servo is not only directly connected to throttle control via a cable but is sometimes responsible for throttle position, it would be more severe than most.

To emphasize a point, if you neglect an active OBD2 fault, you risk not being aware of new fault codes. Even without symptoms, if not monitored, OBD2 error codes can lead to more serious and costly problems.
What Are Some of the Symptoms of the Code?

Symptoms of a P0594 diagnostic code may include:

Inoperative cruise control
Erratic cruise control operation
Vehicle speed is stuck
Limited vehicle speed with cruise control activated
Inaccurate setting of vehicle speed compared to desired or set speed
Specific cruise control functions faulty/erratic

What Are Some of the Common Causes of the Code?

Causes

of this P0594 cruise control code may include:

Faulty/damaged cruise control servo
Cruise control servo cable broken/stuck/disconnected/misadjusted
Wiring problem
ECM (Engine Control Module) problem
Water intrusion module
Connector problem

What Are the Diagnostic and Troubleshooting Steps for P0594?

The first step in the troubleshooting process for any malfunction is to check the Technical Service Bulletins (TSBs) for known issues with the specific vehicle.

Advanced diagnostic steps become very vehicle-specific and may require the appropriate advanced equipment and knowledge to operate accurately. We include the basic steps below, but refer to a repair guide specific to the year/make/model/powertrain for steps specific to your vehicle.
Basic Step #1

Generally speaking, cruise control servos are mounted somewhere in the engine compartment. Most of the time, they are near the throttle body; after all, they control the vehicle’s speed using it. Once located, perform a general visual inspection. Look at the cable, check that it is not fraying, bending, corroding, or showing any signs of malfunction. If the servo cable does not move freely when checking the throttle, the ECM may interpret it as a performance problem.

What does the servo look like? These are typically vacuum-controlled, so their physical condition could indicate a problem. It is important to check all vacuum lines going to the servo itself. Any cracked or deteriorated lines should be considered a sign of your vacuum system’s health. Therefore, I recommend replacing all related vacuum lines as they are inexpensive and could save you problems in the future.
Basic Step #2

On the electrical side of things, check the connector on the servo. Any broken tabs or loose connections should be repaired. The harness may run through tight areas and/or moving parts, so be aware of chafing areas that could cause a problem and repair broken/damaged wires.
Basic Step #3

Depending on the capabilities of your OBD2 scan tool, you can potentially monitor the servo’s operation with it connected to the vehicle. Sometimes, you may receive percentages or electrical values. Regardless, you can compare the values to its physical operation by watching it under the hood, with the wheels on the ground. This is an older procedure that can be problematic, especially when dealing with more modern vehicles. That said, always ensure that diagnostic/repair procedures are also recommended by your vehicle’s manufacturer. If you neglect to do your research here, you could easily damage other vehicle components.

P0595 Low Speed Cruise Control Servo Control Circuit

What Does It Mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles with cruise control. Vehicle makes may include, but are not limited to, Dodge, Chrysler, Ram, Jeep, Hyundai, BMW, Vauxhall, Mini, Chevrolet, etc.

There are many benefits that come with the cruise control function. On long trips, there’s no need to constantly monitor and adjust speeds according to traffic and traffic laws. You press a button or two, and a combination of sensors, solenoids, modules, etc., ensures the vehicle keeps moving at the specified speed until you, or possibly external influences, deactivate or adjust the speed accordingly. Not to mention, the vehicle will have a good idea of how to maintain fuel economy at a good level throughout the journey, as when we drive, we don’t necessarily take everything into account to reduce costs.

Fortunately for us, the ECM (Engine Control Module) is responsible for the smooth but effective operation of the cruise control. The proper functioning of the systems relies on many sensors, switches, modules, VSS, etc. One of them being the cruise control servo. Most of the time, these are responsible for controlling the throttle when you set and/or adjust the cruise control. By controlling the throttle and adjusting accordingly, with this servo, the ECM can adjust the speed easily and effectively. Many times, these servos are mechanically controlled via vacuum lines and throttle cables. The servo’s vacuum is controlled by solenoids, which are in turn controlled by the ECM, which can interpret all other values before specifying throttle position, speed, etc. This fault refers to the circuit involved; refer to the service manual to determine exactly which physical circuit you are working on/diagnosing.

The P0595 Cruise Control Servo Control Circuit Low and related codes (P0525, P0594, and P0596) are set when the ECM monitors a malfunction in the cruise control servo circuit. In the case of P0595 specifically, it is set when a low voltage electrical condition is detected in said circuit.

Example of a Cruise Control Servo:


P0595 Cruise Control Servo
How Severe Is This DTC?

I will set the severity of this code to medium. Regarding most OBD2 error codes for cruise control, they are quite minor. That being said, in this case, because the cruise control servo is not only directly connected to throttle control via a cable but is sometimes responsible for throttle position, it would be more severe than most.

To emphasize a point, if you neglect an active OBD2 fault, you risk not being aware of new fault codes. Even without symptoms, if not monitored, OBD2 error codes can lead to more serious and costly problems.
What Are Some of the Symptoms of the Code?

Symptoms of a P0595 diagnostic code may include:

Inoperative cruise control
Erratic cruise control operation
Vehicle speed is stuck
Limited vehicle speed with cruise control activated
Inaccurate setting of vehicle speed compared to desired or set speed
Specific functions of the cruise control(s) faulty/erratic

What Are Some of the Common Causes of the Code?

Causes

of this P0595 cruise control code may include:

Faulty/damaged cruise control servo
Cruise control servo cable broken/stuck/disconnected/misadjusted
Wiring problem
ECM (Engine Control Module) problem
Water intrusion in the module
Connector problem

What Are the Diagnostic and Troubleshooting Steps for P0595?

The first step in the troubleshooting process for any malfunction is to check the Technical Service Bulletins (TSBs) for known issues with the specific vehicle.

Advanced diagnostic steps become very vehicle-specific and may require the appropriate advanced equipment and knowledge to operate accurately. We include the basic steps below but refer to a repair guide specific to the year/make/model/powertrain for steps tailored to your vehicle.
Basic Step #1

Generally speaking, cruise control servos are mounted somewhere in the engine compartment. Most of the time, they are near the throttle body; after all, they control the vehicle’s speed using it. Once located, perform a general visual inspection. Look at the cable, check that it is not fraying, bending, corroding, or showing any signs of malfunction. If the servo cable does not move freely when checking the throttle, the ECM may interpret it as a performance issue.

What does the servo look like? These are typically vacuum-controlled, so their physical condition could indicate a problem. It is important to check all vacuum lines going to the servo itself. Any cracked or deteriorated lines should be considered a sign of your vacuum system’s health. Therefore, I recommend replacing all related vacuum lines as they are inexpensive and could save you problems in the future.
Basic Step #2

On the electrical side of things, check the connector on the servo. Any broken tabs or loose connections should be repaired. The harness may run through tight areas and/or moving parts, so be aware of chafing areas that could cause a problem and repair broken/damaged wires.
Basic Step #3

Depending on the capabilities of your OBD2 scan tool, you can potentially monitor the servo’s operation with it connected to the vehicle. Sometimes, you may receive percentages or electrical values. Regardless, you can compare the values to its physical operation by watching it under the hood, with the wheels on the ground. This is an older procedure that can be problematic, especially when dealing with more modern vehicles. That said, always ensure that diagnostic/repair procedures are also recommended by your vehicle’s manufacturer. If you neglect to do your research here, you could easily damage other vehicle components.

High Speed Cruise Control Servo Control Circuit

What Does It Mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles with cruise control. Vehicle makes may include, but are not limited to, Dodge, Chrysler, Ram, Jeep, Hyundai, BMW, Vauxhall, Mini, Chevrolet, etc.

There are many benefits that come with the cruise control function. On long trips, there’s no need to constantly monitor and adjust speeds according to traffic and traffic laws. You press a button or two, and a combination of sensors, solenoids, modules, etc., ensures the vehicle keeps moving at the specified speed until you, or possibly external influences, deactivate or adjust the speed accordingly. Not to mention, the vehicle will have a good idea of how to maintain fuel economy at a good level throughout the journey, as when we drive, we don’t necessarily take everything into account to reduce costs.

Fortunately for us, the ECM (Engine Control Module) is responsible for the smooth but effective operation of the cruise control. The proper functioning of the systems relies on many sensors, switches, modules, VSS, etc. One of them being the cruise control servo. Most of the time, these are responsible for controlling the throttle when you set and/or adjust the cruise control. By controlling the throttle and adjusting accordingly, with this servo, the ECM can adjust the speed easily and effectively. Many times, these servos are mechanically controlled via vacuum lines and throttle cables. The servo’s vacuum is controlled by solenoids, which are in turn controlled by the ECM, which can interpret all other values before specifying throttle position, speed, etc. This fault refers to the circuit involved; refer to the service manual to determine exactly which physical circuit you are working on/diagnosing.

The P0596 Cruise Control Servo Control Circuit High and related codes (P0525, P0594, and P0595) are set when the ECM monitors a malfunction in the cruise control servo control circuit. In the case of P0596 specifically, it is set when a high voltage electrical condition is detected in said circuit.

Example of a Cruise Control Servo:


P0596 Cruise Control Servo
How Severe Is This DTC?

I will set the severity of this code to medium. Regarding most OBD2 error codes for cruise control, they are quite minor. That being said, in this case, because the cruise control servo is not only directly connected to throttle control via a cable but is sometimes responsible for the throttle position, it would be more severe than most.

To emphasize a point, if you neglect an active OBD2 fault, you risk not being aware of new fault codes. Even without symptoms, if not monitored, OBD2 error codes can lead to more serious and costly problems.
What Are Some of the Symptoms of the Code?

Symptoms of a P0596 diagnostic code may include:

Inoperative cruise control
Erratic cruise control operation
Vehicle speed is stuck
Vehicle speed limited with cruise control activated
Inaccurate setting of vehicle speed compared to desired or set speed
Specific cruise control functions faulty/erratic

What Are Some of the Common Causes of the Code?

Causes

of this P0596 cruise control code may include:

Faulty/damaged cruise control servo
Cruise control servo cable broken/stuck/disconnected/misadjusted
Wiring problem
ECM (Engine Control Module) problem
Water intrusion module
Connector problem

What Are the Diagnostic and Troubleshooting Steps for P0596?

The first step in the troubleshooting process for any malfunction is to check the Technical Service Bulletins (TSBs) for known issues with the specific vehicle.

Advanced diagnostic steps become very vehicle-specific and may require the appropriate advanced equipment and knowledge to operate accurately. We include the basic steps below but refer to a repair guide specific to the year/make/model/powertrain for steps specific to your vehicle.
Basic Step #1

Generally speaking, cruise control servos are mounted somewhere in the engine compartment. Most of the time, they are near the throttle body; after all, they control the vehicle’s speed using it. Once located, perform a general visual inspection. Look at the cable, check that it is not fraying, bending, corroding, or showing any signs of malfunction. If the servo cable does not move freely when checking the throttle, the ECM may interpret it as a performance issue.

What does the servo look like? These are typically vacuum-controlled, so their physical condition could indicate a problem. It is important to check all vacuum lines going to the servo itself. Any cracked or deteriorated lines should be considered a sign of your vacuum system’s health. Therefore, I recommend replacing all related vacuum lines as they are inexpensive and could save you problems in the future.
Basic Step #2

On the electrical side of things, check the connector on the servo. Any broken tabs or loose connections should be repaired. The harness may run through tight areas and/or moving parts, so be aware of chafing areas that could cause a problem and repair broken/damaged wires.
Basic Step #3

Depending on the capabilities of your OBD2 scan tool, you can potentially monitor the servo’s operation with it connected to the vehicle. Sometimes, you may receive percentages or electrical values. Regardless, you can compare the values to its physical operation by watching it under the hood, with the wheels on the ground. This is an older procedure that can be problematic, especially when dealing with more modern vehicles. That said, always ensure that diagnostic/repair procedures are also recommended by your vehicle’s manufacturer. If you neglect to do your research here, you could easily damage other vehicle components.

P0597 Open Thermostat Heater Control Circuit

What does it mean?

This is a generic powertrain diagnostic trouble code (DTC), meaning it applies to all makes/models from 1996 onward. However, specific troubleshooting steps vary by vehicle.

Codes P0597, P0598, and P0599 all refer to an electronically controlled engine thermostat. These are generic codes, meaning they apply to all vehicles using this type of thermostat control, though only a small number of manufacturers use this system. Therefore, this trouble code article is essentially identical for all three codes.

Engine code P0597 indicates a failure has occurred in this system where the control voltage is absent. Mostly, vehicles manufactured in Germany such as BMW, Mercedes, Audi, Mini, Volkswagen, Opel, and Jaguar use this system.

The electronically controlled thermostat consists of various temperature and load sensors, a computer program, and the control unit with an integrated thermostat.
Concept

By electronically controlling coolant flow or engine temperature, partial throttle increases fuel economy and reduces emissions, while lowering temperature under load increases power.

Symptoms

Symptoms vary depending on the thermostat’s position at the time of failure, but there is unlikely to be a noticeable difference in vehicle operation.

    The check engine light illuminates and one of the above codes is set
    The temperature gauge may read abnormally high if the thermostat failed in a partially closed position; conversely, it will read lower than normal if the thermostat failed in a fully open position

Potential Causes

Experience shows the issue is usually a loose or corroded electrical connector or the electric thermostat itself is at fault. Sometimes the Motronic computer (engine management) fails, but this is the least likely cause.

    A loose or corroded connector on the thermostat
    A coolant leak will trigger the code
    The thermostat itself has failed
    A short circuit or open circuit has occurred in the wiring harness between the computer and the thermostat
    The Motronic computer has failed

Diagnostic and Repair Procedures for Code P0597

    Remove and inspect the electrical connector. Eliminate any corrosion using baking soda or by scraping. Apply electrical grease and ensure a tight connection.
    Inspect the coolant level in the radiator. Low coolant levels will set a code by causing the electronic thermostat to overheat.
    Remove the electrical connector and check the resistance values on the thermostat. For this procedure, you will need a service manual or the necessary information available online.

This information should include pin identification and location, wire colors, pin values in volts at specific temperatures and resistances. These values and the diagnostic flow vary by manufacturer and engine size.

You will also need an infrared temperature probe and a volt/ohmmeter.

    Determine the engine temperature with the temperature probe
    Start the engine and test the voltage on the Motronic side of the harness as per instructions. If it is within limits, continue testing. If there was no voltage or it was out of range, replace the Motronic unit
    Compare the resistance on the thermostat side of the harness to the thermostat. If the resistance is out of range, replace the thermostat unit
    If tools are not readily available, take the vehicle to a reputable shop that has access to the necessary information. This is a simple diagnosis with the right tools

P0598 Low Thermostat Heater Control Circuit

What does it mean?

This is a generic powertrain diagnostic trouble code (DTC), meaning it covers all makes/models from 1996 onward. However, specific troubleshooting steps vary by vehicle.

Codes P0597, P0598, and P0599 all refer to an electronically controlled engine thermostat. These are generic codes, meaning they apply to all vehicles using this type of thermostat control, though only a small number of manufacturers use such systems. Therefore, this trouble code article is essentially identical for all three codes.

Diagnostic code P0598 indicates a failure in this system where the control voltage is low. Mostly, vehicles manufactured in Germany such as BMW, Mercedes, Audi, Mini, Volkswagen, Opel, and Jaguar use this system.

The electronically controlled thermostat consists of various temperature and load sensors, a computer program, and the control unit with an integrated thermostat.
Concept

By electronically controlling coolant flow or engine temperature, partial throttle increases fuel economy and reduces emissions, while reducing temperature under load increases power.

Symptoms

Symptoms vary depending on the thermostat’s position at the time of failure; however, there is unlikely to be a noticeable difference in vehicle operation.

    The check engine light comes on and one of the above codes is set
    The temperature gauge may read abnormally high if the thermostat failed in a partially closed position; conversely, it will read lower than normal if the thermostat failed in a fully open position

Potential Causes

Experience shows that the issue is usually a loose or corroded electrical connector or the electric thermostat itself is at fault. Sometimes the Motronic computer (engine management) fails, but this is the least likely cause.

    A loose or corroded connector on the thermostat
    A coolant leak will trigger the code
    The thermostat itself has failed
    A short circuit or open circuit occurred in the wiring harness between the computer and the thermostat
    The Motronic computer has failed

Diagnostic and Repair Procedures

    Remove and inspect the electrical connector. Eliminate any corrosion using baking soda or by scraping. Apply electrical grease and confirm a tight connection.
    Inspect the coolant level in the radiator. Low coolant levels will set a code by causing the electronic thermostat to overheat.
    Remove the electrical connector and check the resistance values on the thermostat. For this procedure, you will need a service manual or the necessary information available online.

This information should include pin identification and location, wire colors, pin voltage values at specific temperatures, and resistances. These values and the diagnostic flow vary by manufacturer and engine size.

You will also need an infrared temperature probe and a volt/ohmmeter.

    Determine the engine temperature with the temperature probe
    Start the engine and test the voltage on the Motronic side of the harness as per instructions. If it is within limits, continue testing. If there was no voltage or it was out of range, replace the Motronic unit
    Compare the resistance on the thermostat side of the harness to the thermostat. If the resistance is out of range, replace the thermostat unit
    If tools are not readily available, take the vehicle to a reputable shop that has access to the necessary information. This is a simple diagnosis with the right tools

High Thermostat Heater Control Circuit

What does it mean?

This is a generic powertrain diagnostic trouble code (DTC), meaning it covers all makes/models from 1996 onward. However, specific troubleshooting steps vary by vehicle.

Codes P0597, P0598, and P0599 all refer to an electronically controlled engine thermostat. These are generic codes, meaning they apply to all vehicles using this type of thermostat control, though only a small number of manufacturers use this system. Therefore, this trouble code article is essentially identical for all three codes.

Code P0599 indicates a failure has occurred in this system where the control voltage is high. Mostly, vehicles manufactured in Germany such as BMW, Mercedes, Audi, Mini, Volkswagen, Opel, and Jaguar use this system.

The electronically controlled thermostat consists of various temperature and load sensors, a computer program, and the control unit with an integrated thermostat.
Concept

By electronically controlling the coolant flow or engine temperature, partial throttle increases fuel economy and reduces emissions, while reducing temperature under load increases power.

Symptoms

Symptoms of a P0599 code vary depending on the thermostat’s position at the time of failure; however, it’s unlikely there will be a noticeable difference in vehicle operation.

    The check engine light comes on and one of the above codes is set
    The temperature gauge may read abnormally high if the thermostat failed in a partially closed position; conversely, it will read lower than normal if the thermostat failed in a fully open position

Potential Causes

Experience shows the problem is usually a loose or corroded electrical connector or that the electric thermostat itself is at fault. Sometimes the Motronic computer (engine management) fails, but this is the least likely cause.

    A loose or corroded connector on the thermostat
    A coolant leak will trigger the code
    The thermostat itself has failed
    A short circuit or open circuit has occurred in the wiring harness between the computer and the thermostat
    The Motronic computer has failed

Diagnostic and Repair Procedures

    Remove and inspect the electrical connector. Eliminate any corrosion using baking soda or by scraping. Apply electrical grease and confirm a tight connection.
    Inspect the coolant level in the radiator. Low coolant levels will set a code by causing the electronic thermostat to overheat.
    Remove the electrical connector and check the resistance values on the thermostat. For this procedure, you will need a service manual or the necessary information available online.

This information should include pin identification and location, wire colors, pin values in volts at specific temperatures and resistances. These values and the diagnostic flow vary by manufacturer and engine size.

You will also need an infrared temperature probe and a volt/ohmmeter.

    Determine the engine temperature with the temperature probe
    Start the engine and test the voltage on the Motronic side of the harness according to instructions. If it is within limits, continue testing. If there was no voltage or it was out of range, replace the Motronic unit
    Compare the resistance on the thermostat side of the harness to the thermostat. If the resistance is out of range, replace the thermostat unit
    If tools are not readily available, take the vehicle to a good shop that has access to the necessary information. This is a simple diagnosis with the right tools