Excessive Exhaust Gas Recirculation B Flow Detected

Understanding Error Code P049C: Excessive Flow Detected in EGR System “B”

Introduction

What does the P049C code mean? (General definition: the PCM has detected excessive flow in the “B” circuit of the EGR system for a specific downgrade setting).
This is a generic powertrain diagnostic trouble code (DTC) applicable to OBD-II equipped vehicles with an Exhaust Gas Recirculation (EGR) system.
Examples of affected brands: Dodge, Ford, Toyota, Chevrolet, Nissan, VW, Audi, Mazda, Mitsubishi, Subaru, etc.
Important: Precise repair steps may vary depending on the year, make, model, and powertrain configuration.
The “B” designation refers to a specific position of the EGR valve in the downgraded state.
An electrical or mechanical problem can cause the P049C code to be stored.

Downgraded EGR System Operation and Importance

The downgraded EGR valve system is essential for reducing nitrogen oxide (NOx) emissions produced by the internal combustion of diesel engines.
NOx contributes to the depletion of the ozone layer.
NOx emissions are regulated by federal mandates in North America.
The downgraded EGR system recirculates a portion of the exhaust gases to the intake manifold in measured increments for a second combustion.

EGR Flow Monitoring

EGR system flow is monitored by different methods:
- DPFE Sensor (Differential Pressure Feedback EGR): Measures pressure in the tube connecting the EGR valve and the exhaust manifold. Valve opening increases pressure and sensor voltage.
- MAP Sensor (Manifold Absolute Pressure): In some applications, a proportional change in MAP sensor voltage is expected when the PCM commands the downgraded EGR to open to a certain level.
- MAT Sensor (Manifold Air Temperature): Some vehicles use the MAT sensor to detect the temperature increase when hot exhaust gases recirculate into the intake manifold.
The P049C code is stored and the Malfunction Indicator Lamp (MIL) may illuminate if the PCM does not detect the expected change from the “B” EGR flow monitoring sensor system, indicating an excessively high flow.
Several ignition cycles with the fault may be required for the MIL to illuminate on some vehicles.

Severity of DTC P049C

Conditions contributing to a P049C code can affect overall engine performance and fuel efficiency.
This code should be classified as severe.

Possible Symptoms of Code P049C

List of associated symptoms:
- Decreased engine performance
- Excessively rich or lean exhaust
- Delayed engine starting (especially when cold)
- Reduced fuel efficiency

Common Causes of Code P049C

List of possible causes:
- Faulty EGR valve
- EGR passage(s) clogged with carbon deposits
- Collapsed or cracked DPFE hoses
- Faulty DPFE, MAP, or MAT sensor
- Open or shorted circuits to the EGR valve or associated sensors

P049C Troubleshooting Steps

Step 1: Retrieving codes and freeze frame data:
- Start by locating the vehicle’s diagnostic connector and use a scanner to retrieve all stored codes.
- Note this information for future reference.
- Test drive the vehicle to see if the P049C code resets immediately.
Step 2: Consulting Technical Service Bulletins (TSBs):
- Search the vehicle’s TSBs for entries matching the vehicle, stored codes, and symptoms. TSBs may contain helpful diagnostic tips from specialists.
Step 3: Preparing tools and information:
- If the P049C code is stored after clearing, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information (wiring diagrams, component specifications).
Step 4: Visual inspection:
- Visually inspect the EGR valve, all associated wiring, and connectors.
- Pay close attention to wiring harnesses located near hot exhaust manifolds and the sharp edges of heat shields.
Step 5: Precautions before electrical testing:
- To avoid damaging control modules, disconnect all associated control modules from the circuit before testing resistance or continuity with the DVOM.
Step 6: Testing manual activation of the EGR system:
- Use the scanner to manually activate the EGR system (note that most systems require a certain speed for automatic activation).
Step 7: Testing EGR valve circuits:
- Using wiring diagrams and connector pinout charts (from your information source), test each circuit of the EGR valve connector with the DVOM.
- Circuits not matching manufacturer specifications must be traced back to their source (usually the PCM connector) and retested.
- If no PCM output signal is detected, suspect a PCM programming issue or a faulty PCM.
- Repair or replace open or shorted circuits as necessary.
Step 8: Testing the EGR valve and associated sensors:
- If all circuits meet specifications, use the DVOM to test the EGR valve itself and the associated sensors (DPFE, MAP, MAT).
- Your vehicle information source will provide the testing procedures and specifications for these components.
- Replace the downgraded EGR valve and/or associated sensors if they do not meet manufacturer specifications.
Important note: This code (P049C) should only appear on vehicles equipped with downgradable EGR valve systems.

P049D EGR A Control Position Exceeded Learning Limit

Exhaust Gas Recirculation A Control Position Exceeded Learning Limit

What does this mean?

This is a generic diagnostic trouble code (DTC) for the powertrain that generally applies to OBD-II equipped vehicles with an Exhaust Gas Recirculation (EGR) system. This may include, but is not limited to, vehicles from Dodge/Ram (Cummins), Chevy/GMC (Duramax), Honda, Jeep, Hyundai, etc.

Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your OBD-II equipped vehicle has stored a P049D code, it means the Powertrain Control Module (PCM) has detected a malfunction in a certain control position of the exhaust gas recirculation (EGR) valve. It referred to a specific position of the EGR valve.

The EGR valve system is designed to recirculate a portion of the spent exhaust gases back to the intake manifold, in measured increments, so it can be burned a second time. This process is essential in reducing nitrogen oxide (NOx) particles that are released into the atmosphere as a byproduct of internal combustion and diesel engine operation. NOx is suspected to be a contributing factor to the depletion of the ozone layer from exhaust emissions. NOx emissions are regulated by federal mandate in North American vehicles.

The learning limit is a programmed degree that reflects the minimum and maximum parameters to which a certain position (A) of the EGR valve can adapt. If the PCM detects that the actual EGR valve position is beyond these parameters, a P049D code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated. In some vehicle applications, multiple ignition cycles (with a fault) are required for the MIL to illuminate.
How severe is this DTC?

Since the P049D code pertains to the EGR system, it should not be considered severe.
What are some of the symptoms of the code?

Symptoms of a P049D fault code may include:

There will likely be no symptoms associated with this code
Slightly decreased fuel efficiency
Possible drivability issues

What are some of the common causes of the code?

Causes

of this P049D code may include:

Faulty EGR valve
Faulty EGR sensor
Incorrect PCM or PCM programming error

What are the troubleshooting steps for P049D?

I would typically begin my diagnosis by locating the vehicle’s diagnostic connector and retrieving all stored codes and associated data. I would write down all this information in case I need it as I proceed with my diagnosis. Then, I would test the vehicle to see if the code immediately resets.

By searching the vehicle’s Technical Service Bulletins (TSBs) for entries that match the vehicle, stored codes, and displayed symptoms, you may discover the solution to your (potentially difficult) diagnosis. Since TSB entries come from thousands of repair specialists, they often contain very helpful details.

If P049D is stored after clearing the codes, I would have access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.

Now, I would perform a visual inspection of the EGR valve and all associated wiring and connectors. Focus on wiring harnesses that are routed near hot exhaust components and the sharp edges often associated with heat shields.

NOTE: Disconnect all associated controllers from the circuit before testing resistance/continuity with the DVOM.

Using wiring diagrams and connector pinout charts, located in your vehicle information source, test each EGR valve connector circuit (with the DVOM) for the proper signal. It may be necessary to manually activate the EGR system using the scanner, as most systems require a defined vehicle speed before automatic activation can occur. Circuits that do not meet manufacturer specifications will need to be traced back to the source (usually the PCM connector) and retested. If the PCM output signal is not detected, suspect a PCM programming error or faulty PCM. Otherwise, repair or replace open/short-circuited circuits as needed.

Use the DVOM to test the actual EGR valve and integrated sensors if all circuits meet manufacturer specifications. Your vehicle information source will again provide information for testing this component. If the EGR valve and all (integrated) sensors do not align with manufacturer specifications, suspect it is faulty.

This code should only be displayed in vehicles equipped with an EGR valve.

P049E EGR B Control Position Exceeded Learning Limit

Exhaust Gas Recirculation B Position Control Learning Limit Exceeded

What does that mean?

This is a generic diagnostic trouble code (DTC) for the powertrain that generally applies to OBD-II vehicles equipped with an Exhaust Gas Recirculation (EGR) system. This may include, but is not limited to, vehicles from Dodge/Ram (Cummins), Chevy/GMC (Duramax), Honda, Jeep, Hyundai, etc.

Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

If your OBD-II equipped vehicle has stored a P049E code, it means the Powertrain Control Module (PCM) has detected a malfunction in a specific position control of the lowered Exhaust Gas Recirculation (EGR) valve. B refers to a specific position of the lowered EGR valve.

The lowered EGR valve system is designed to recirculate a portion of the spent exhaust gases back into the intake manifold, in measured increments, so it can be burned a second time. This process is essential in reducing nitrogen oxide (NOx) particles that are released into the atmosphere as a byproduct of internal combustion and diesel engine operation. NOx is suspected to be a contributing factor to the depletion of the ozone layer from exhaust emissions. NOx emissions are regulated by federal mandate in North American vehicles.

The learning limit is a programmed degree that reflects the minimum and maximum parameters to which a specific position (B) of the lowered EGR valve can adapt. If the PCM detects that the actual position of the EGR valve is beyond these parameters, a P049E code will be stored and a Malfunction Indicator Lamp (MIL) may illuminate. In some vehicle applications, multiple ignition cycles (with a fault) are required for the MIL to light up.
How severe is this DTC?

Since the P049E code relates to the EGR system, it should not be considered severe.
What are some of the symptoms of the code?

Symptoms of a P049E fault code may include:

There will likely be no symptoms associated with this code
Slightly decreased fuel efficiency
Possible driving issues

What are some common causes of the code?

Causes

of this P049E code may include:

Faulty EGR valve
Faulty EGR sensor
Incorrect PCM or PCM programming error

What are the troubleshooting steps for P049E?

I would typically start my diagnosis by locating the vehicle’s diagnostic connector and retrieving all stored codes and associated data. I would write down all this information in case I need it as I proceed with my diagnosis. Then, I would test the vehicle to see if the code resets immediately.

By searching the vehicle’s Technical Service Bulletins (TSBs) for entries matching the vehicle, stored codes, and displayed symptoms, you might discover the solution to your (potentially difficult) diagnosis. Since TSB entries come from thousands of repair specialists, they often contain very helpful details.

If the P049E is stored after clearing the codes, I would have access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.

Now, I would perform a visual inspection of the EGR valve and all associated wiring and connectors. Focus on wiring harnesses routed near hot exhaust components and the sharp edges often associated with exhaust shields.

NOTE: Disconnect all associated controllers from the circuit before testing resistance/continuity with the DVOM.

Using wiring diagrams and connector pinout charts, located in your vehicle information source, test each EGR valve connector circuit (with the DVOM) for the appropriate signal. It may be necessary to manually activate the EGR system using the scanner, as most systems require a defined speed before automatic activation can occur. Circuits that do not meet manufacturer specifications will need to be traced back to the source (usually the PCM connector) and retested. If the PCM output signal is not detected, suspect a PCM programming error or faulty PCM. Otherwise, repair or replace open/short-circuited circuits as needed.

Use the DVOM to test the actual EGR valve and integrated sensors if all circuits meet manufacturer specifications. Your vehicle information source will again provide information for testing this component. If the lowered EGR valve and all (integrated) sensors do not align with manufacturer specifications, suspect it is faulty.

This code should only appear in vehicles equipped with a lowered EGR valve.

Exhaust Pressure Control Valve B

What does it mean?

This generic powertrain/diagnostic engine code generally applies to diesel engines, including but not limited to certain Ford, Dodge, Mercedes, Nissan, and VW vehicles.

A valve is placed in the exhaust stream after the exhaust manifold to generate heat in the form of backpressure in the exhaust. This heat and/or backpressure can be used to assist with cold starting. It can also be used to oppose cylinder pressure from the engine cylinders to the exhaust, thereby slowing the engine and the vehicle with it. This is particularly useful during towing operations.

This code strictly pertains to the exhaust pressure control solenoid output circuit. This code is considered an electrical circuit fault only.

Troubleshooting steps may vary depending on the manufacturer, type of exhaust backpressure control, and the color of the control solenoid wires. Refer to a vehicle-specific repair manual to determine which is the “B” valve in your particular case.

Symptoms

Symptoms of a P049F engine code may include:

Malfunction Indicator Light (MIL) illuminated
Lack of power
Absence of engine braking
Longer than normal cold engine warm-up time

Potential Causes of P049F

Typically, the causes for this code to set are:

Short to power in the supply circuit between the exhaust pressure control solenoid and the PCM (Powertrain Control Module)
Open in the supply circuit between the exhaust pressure control solenoid and the PCM
Short to ground in the exhaust pressure control solenoid supply circuit
Faulty exhaust pressure control solenoid
Possibly a failed PCM (highly unlikely)

Diagnostic and Repair Procedures

A good starting point is always to search for a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogramming to address this issue, and it’s worth checking before discovering you’ve taken a long/wrong path.

Next, locate the “B” exhaust pressure control solenoid on your particular vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burns, or melted plastic. Separate the connectors and carefully inspect the terminals (the metal parts) inside the connectors. See if they appear corroded, burnt, or perhaps greenish compared to the normal metal color you’re used to seeing. You can get electrical contact cleaner at any auto parts store if terminal cleaning is needed. If that’s not possible, find 91% rubbing alcohol and a soft plastic-bristled brush to clean them. Then, let them air dry, get some dielectric silicone compound (the same used for bulb sockets and spark plug wires), and apply it where the terminals make contact.

If you have a scan tool, clear the diagnostic codes from memory and see if this code returns. If not, the connections were likely your problem.

If the code returns, we’ll need to test the solenoid and its associated circuits. Typically, there are 2 wires to the exhaust pressure control solenoid. First, disconnect the wiring harness from the exhaust pressure control solenoid. With a digital volt-ohm meter (DVOM), connect one meter lead to one terminal of the solenoid. Connect the remaining meter lead to the other terminal of the solenoid. It should not be open or shorted. Check the resistance specifications for your specific vehicle. If the solenoid is open or shorted (infinite resistance or no resistance/0 ohms), replace the solenoid.

If that’s okay, with a DVOM, check that the exhaust pressure control solenoid supply circuit has 12V (red lead to the solenoid supply circuit, black lead to a good ground). Ensure the ignition is on. If there is no 12 volts at the solenoid, or if there is 12 volts when the ignition is off, repair the wiring from the PCM or relay to the solenoid, or possibly a faulty PCM.

If that checks out, verify that the exhaust pressure control solenoid is properly grounded. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the exhaust pressure control solenoid circuit ground. If the test light does not illuminate, that would indicate a circuit problem. If it lights up, wiggle the wiring harness going to each sensor to see if the test light flickers, indicating an intermittent connection.

If all tests have passed so far and you continue to get a P049F code, it would most likely indicate a failing exhaust pressure control solenoid, although a faulty PCM cannot be ruled out until the solenoid has been replaced.

P04A0 Exhaust Pressure Regulator Valve B Range / Performance

Exhaust Pressure Control Valve “B” Range/Performance

What does it mean?

This generic powertrain/engine diagnostic code typically applies to diesel engines, including but not limited to certain Ford, Dodge, Mercedes, Nissan, and VW vehicles.

This code may also apply to trucks equipped with diesel engines and dealer-installed exhaust brakes.

A valve is placed in the exhaust stream after the exhaust manifold to generate heat in the form of backpressure in the exhaust. This heat and/or backpressure can be used to assist with cold starts. It can also be used to oppose cylinder pressure from the engine’s cylinders to the exhaust, thereby slowing the engine and the vehicle with it. This is particularly useful during towing operations.

This code is strictly concerned with the incoming signal from the exhaust pressure sensor that does not match the intake manifold pressure, ambient air pressure, or preprogrammed information during normal driving. It could be a mechanical or electrical circuit fault, depending on the vehicle manufacturer.

Troubleshooting steps may vary depending on the manufacturer, the type of exhaust backpressure control, and the color of the control solenoid wires. Refer to a vehicle-specific repair manual to determine which is the “B” valve in your particular case.

Symptoms

Symptoms of a P04A0 engine code may include:

Malfunction Indicator Lamp (MIL) illuminated
Lack of power
Absence of engine braking
Cold engine warm-up time longer than normal

Potential Causes of P04A0

Typically, the causes for this code to set are:

Stuck exhaust backpressure valve
Possibly stuck/damaged/misadjusted turbocharger deflector
Exhaust system restriction/leak
Exhaust gas pressure sensor
Possibly failed PCM (highly unlikely)

Diagnostic and Repair Procedures

Next, check for any exhaust leaks. Listen for exhaust noise from all manifolds and exhaust pipes and look for the presence of black soot at the leak location. If there is a leak, repair the exhaust leak first.

Then, locate the “B” exhaust pressure sensor on your specific vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, scraping, bare wires, burns, or melted plastic. Disconnect the connectors and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt, or perhaps greenish compared to the normal metal color you are probably used to seeing. You can get electrical contact cleaner at any auto parts store if terminal cleaning is needed. If that’s not possible, find 91% isopropyl alcohol and a soft plastic-bristled brush to clean them. Then, let them air dry, get some dielectric silicone compound (the same kind used for light bulb sockets and spark plug wires), and apply a small amount where the terminals make contact.

Additionally, if your vehicle is equipped, remove the sensing tube that connects the exhaust backpressure sensor to the exhaust manifold. Try blowing through it. If you cannot, this is also a possible cause of this code.

If you have a scan tool, clear the diagnostic codes from the memory and see if this code returns. If it does not, the connections were likely your problem.

If the code returns, you will need to check the proper operation of the turbocharger boost. You will need a scan tool capable of reading the turbocharger boost pressure. You may need to monitor the intake manifold pressure, as this will provide the same information. Note the pressure at Key On, Engine Off. After that, start the engine, drive the vehicle to a safe speed, then momentarily accelerate the engine to full throttle, ensuring the engine speed does not exceed 2500-3000 RPM. You should note a change of at least 18 PSI, perhaps more depending on the vehicle manufacturer and the vehicle’s model year. If you cannot achieve a boost pressure of at least 18 psi, a faulty/misadjusted/stuck wastegate, an exhaust restriction, or possibly a faulty turbocharger is indicated.

If this test was successful, or if you were unable to check the turbocharger boost, we will need to test the sensor and its associated circuits. Typically, there are 3 wires at the exhaust pressure sensor.

Disconnect the harness going to the exhaust pressure sensor. With a digital voltmeter (DVOM), test the 5V supply circuit going to the sensor to ensure it is powered (red lead to the 5V supply circuit, black lead to a good ground). If there are 12 volts at the sensor when there should be 5 volts, repair the wiring from the PCM to the sensor for a short to 12 volts, or possibly a faulty PCM.

If that’s okay, with a DVOM, check that the exhaust pressure sensor signal circuit is at 5V (red lead to the sensor signal circuit, black lead to a good ground). If there is no 5 volts at the sensor, or if you see 12 volts at the sensor, repair the wiring from the PCM to the sensor, or again a faulty PCM.

If that checks out, verify that the exhaust pressure sensor ground is good. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the exhaust pressure sensor circuit ground. If the test light does not illuminate, this would indicate a circuit problem. If it lights up, wiggle the wire harness going to the exhaust pressure sensor to see if the test light flickers, indicating an intermittent connection.

If all tests have passed so far and you continue to get a P04A0 code, this would most likely indicate a failing exhaust pressure sensor, although a faulty PCM cannot be ruled out until the sensor has been replaced.

P04A1 Exhaust Pressure Control Valve B Low

What Does It Mean?

This generic powertrain/diagnostic engine code generally applies to diesel engines, including but not limited to certain Ford, Dodge, Mercedes, Nissan, and VW vehicles.

This code may also apply to trucks equipped with diesel engines and dealer-installed exhaust brakes.

A valve is placed in the exhaust stream after the exhaust manifold to generate heat in the form of backpressure in the exhaust. This heat and/or backpressure can be used to assist with cold starts. It can also be used to oppose cylinder pressure from the engine’s cylinders to the exhaust, thereby slowing the engine and the vehicle with it. This is particularly useful during towing operations.

This code is strictly concerned with the incoming signal from the exhaust pressure sensor that does not match the intake manifold pressure or ambient air pressure during normal driving. It could be a mechanical or electrical circuit fault, depending on the vehicle manufacturer.

Symptoms

Symptoms of a P04A1 engine code may include:

    Malfunction Indicator Lamp (MIL) illuminated
    Lack of power
    Lack of engine braking
    Cold engine warm-up time longer than normal

Potential Causes of P04A1

Typically, the causes for this code to set are:

    Short to power in the power circuit between the exhaust pressure control solenoid and the PCM (Powertrain Control Module)
    Open in the power circuit between the exhaust pressure control solenoid and the PCM
    Short to ground in the exhaust pressure control solenoid power circuit
    Faulty exhaust pressure control relay
    Faulty exhaust pressure control solenoid
    Possibly a failed PCM (highly unlikely)

Diagnostic and Repair Procedures

A good starting point is always to search for a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogram to cover this issue, and it’s worth checking before finding out you’ve taken a long/wrong path. PCM = Powertrain Control Module.

Next, locate the “B” exhaust pressure control solenoid on your specific vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burns, or melted plastic. Disconnect the connectors and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt, or perhaps green in color compared to the normal metal color you’re probably used to seeing. You can get electrical contact cleaner at any auto parts store if terminal cleaning is needed. If that’s not possible, find 91% rubbing alcohol and a light plastic-bristled brush to clean them. Then let them air dry, get some dielectric silicone compound (same as used for light bulb sockets and spark plug wires), and apply a bit where the terminals make contact.

If you have a scan tool, clear the diagnostic codes from memory and see if this code returns. If it doesn’t, the connections were likely your problem.

If the code returns, locate the relay that operates the exhaust pressure control solenoid. This relay may also be called an exhaust brake or engine brake relay. Once located, swap it with an identical relay in the relay/fuse box that you know is working. Clear the codes and see if this code returns. If it doesn’t, the relay was likely your problem.

If the code returns, we will need to test the solenoid and its associated circuits. Typically, there are 2 wires to the exhaust pressure control solenoid. First, disconnect the wiring harness from the exhaust pressure control solenoid. With a digital volt ohm meter (DVOM), connect one meter lead to one terminal of the solenoid. Connect the remaining meter lead to the other terminal of the solenoid. It should not be open or shorted. Check the resistance specifications for your specific vehicle. If the solenoid is open or shorted (infinite resistance or no resistance/0 ohms), replace the solenoid.

If that’s okay, with a DVOM, check that the exhaust pressure control solenoid power circuit is 12V (red lead to the solenoid power circuit, black lead to a good ground). Ensure the ignition is on. If there is no 12 volts at the solenoid, or if there is 12 volts when the ignition is off, repair the wiring from the PCM or relay to the solenoid, or possibly a faulty PCM.

If that’s okay, check that the exhaust pressure control solenoid ground is good. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the exhaust pressure control solenoid circuit ground. If the test light does not illuminate, that would indicate the circuit problem. If it lights, wiggle the wiring harness going to each sensor to see if the test light flickers, indicating an intermittent connection.

If all tests have passed so far and you continue to get a P04A1 code, it would most likely indicate a failing exhaust pressure control solenoid, although a faulty PCM cannot be ruled out until the solenoid has been replaced.

P04A2 Exhaust Pressure Control Valve B High

High “B” Exhaust Pressure Control Valve

What does it mean?

This generic powertrain/engine diagnostic code typically applies to diesel engines, including but not limited to certain Ford Powerstroke, Dodge Cummins, Mercedes, Nissan, and VW vehicles.

This code may also apply to trucks equipped with diesel engines and dealer-installed exhaust brakes.

A valve is placed in the exhaust stream after the exhaust manifold to generate heat in the form of backpressure in the exhaust. This heat and/or backpressure can be used to assist with cold starts. It can also be used to oppose cylinder pressure from the engine’s cylinders to the exhaust, thereby slowing the engine and the vehicle with it. This is particularly useful during towing operations.

Symptoms

Symptoms of a P04A2 engine code may include:

Malfunction Indicator Lamp (MIL) illuminated
Lack of power
Absence of engine braking
Longer than normal cold engine warm-up time

Potential Causes of P04A2

Typically, the causes for this code to set are:

Stuck exhaust backpressure valve
Restricted exhaust
Open in the ground circuit to the exhaust pressure sensor
Open in the signal circuit between the exhaust pressure sensor and the PCM
Short to voltage in the exhaust pressure sensor signal circuit
Faulty exhaust pressure sensor – internal short to voltage
Clogged exhaust pressure sensor sensing tube
Possibly turbocharger overboost
Possibly the PCM has failed (highly unlikely)

Diagnostic and Repair Procedures

A good starting point is always to search for a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogram to address this issue, and it’s worth checking before discovering you’ve taken a long/wrong path. PCM = Powertrain Control Module.

Next, locate the “B” exhaust pressure sensor on your specific vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burns, or melted plastic. Disconnect the connectors and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt, or perhaps greenish compared to the normal metal color you’re probably used to seeing. You can get electrical contact cleaner at any auto parts store if terminal cleaning is needed. If that’s not available, find 91% isopropyl alcohol and a soft plastic-bristled brush to clean them. Then let them air dry, get some dielectric silicone compound (the same kind used for bulb sockets and spark plug wires) and apply a small amount where the terminals make contact.

Additionally, if your vehicle is equipped, remove the sensing tube that connects the exhaust backpressure sensor to the exhaust manifold. Try blowing through it. If it’s blocked, this is also a possible cause of this code.

If you have a scan tool, clear the diagnostic codes from memory and see if this code returns. If it doesn’t, the connections were likely your problem.

If the code returns, you’ll need to check the proper operation of the turbocharger overboost. You will need a scan tool capable of reading the turbocharger overboost pressure. You may need to monitor the intake manifold pressure, as this will provide the same information. Note the pressure with the Key in the On position, but with the engine off. After that, start the engine, drive the vehicle to a safe speed, then momentarily accelerate the engine to full throttle, ensuring the engine RPM does not exceed 2500-3000 RPM. You should note a change of at least 18 PSI, perhaps more depending on the vehicle manufacturer and the vehicle’s model year.

If this test was successful, or if you were unable to check the turbocharger overboost, we will need to test the sensor and its associated circuits. Typically, there are 3 wires at the exhaust pressure sensor.

Disconnect the harness going to the exhaust pressure sensor. With a Digital Volt-Ohm Meter (DVOM), test the 5V supply circuit going to the sensor to ensure it is powered (red lead to the 5V supply circuit, black lead to a good ground). If there are 12 volts at the sensor when there should be 5 volts, repair the wiring from the PCM to the sensor for a short to 12 volts, or possibly a faulty PCM.

If that checks out, verify that the exhaust pressure sensor is properly grounded. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the exhaust pressure sensor circuit ground. If the test light does not illuminate, this would indicate a circuit problem. If it lights up, wiggle the wire harness going to the exhaust pressure sensor to see if the test light flickers, indicating an intermittent connection.

If all the previous tests were successful and you continue to get a P04A2 code, this would most likely indicate a failing exhaust pressure sensor, although a stuck closed exhaust backpressure valve or a failing PCM cannot be ruled out until the sensor has been replaced.

P04A3 Intermittent Exhaust Pressure Control Valve B

What does it mean?

This generic powertrain/drivetrain diagnostic code generally applies to diesel engines, including but not limited to certain Ford, Dodge, Mercedes, Nissan, and VW vehicles.

This code may also apply to trucks equipped with diesel engines and dealer-installed exhaust brakes.

A valve is placed in the exhaust stream after the exhaust manifold to generate heat in the form of backpressure in the exhaust. This heat and/or backpressure can be used to assist with cold starts. It can also be used to oppose cylinder pressure from the engine’s cylinders to the exhaust, thereby slowing the engine and the vehicle with it. This is particularly useful during towing operations.

Symptoms

Symptoms of a P04A3 engine code may include:

Malfunction Indicator Lamp (MIL) illuminated
Lack of power
Absence of engine braking
Cold engine warm-up time longer than normal

Potential Causes of P04A3

Typically, the causes for this code to set are:

Blockage in the exhaust manifold tube to the pressure sensor
Exhaust system / air intake / boost air leaks
Intermittent open in the exhaust pressure sensor ground circuit
Intermittent open in the signal circuit between the exhaust pressure sensor and the PCM (Powertrain Control Module)
Intermittent short to voltage in the signal circuit to the exhaust pressure sensor
Exhaust gas pressure sensor
Possibly turbocharger overboost
Possibly the PCM has failed (highly unlikely)

Diagnostic and Repair Procedures

A good starting point is always to search for a Technical Service Bulletin (TSB) for your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogramming to cover this issue, and it is worth checking before discovering you’ve taken a long/wrong path. PCM = Powertrain Control Module.

Next, locate the “B” exhaust pressure sensor on your specific vehicle. Once located, disconnect the tube connecting the sensor to the exhaust manifold. Try to blow through it. If you cannot, try to pass a small piece of wire through it to dislodge the carbon trapped inside, causing the error code you are experiencing.

If the tube is clear and free, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burns, or melted plastic. Separate the connectors and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt, or perhaps greenish compared to the normal metallic color you are probably used to seeing. You can get electrical contact cleaner at any auto parts store if terminal cleaning is needed. If that is not possible, find 91% rubbing alcohol and a light plastic-bristled brush to clean them. Then, let them air dry, get some dielectric silicone compound (the same stuff used for light bulb sockets and spark plug wires), and apply it where the terminals make contact.

If you have a scan tool, clear the diagnostic codes from the memory and see if this code returns. If it does not, the connections were likely your problem.

If the code returns, you will need to check the proper operation of the turbocharger overboost. You will need a scan tool capable of reading the turbocharger boost pressure. You may need to monitor the intake manifold pressure, as this will provide the same information. Note the pressure at Key On, but with the engine off. After that, start the engine, drive the vehicle to a safe speed, then momentarily accelerate the engine to full throttle, ensuring the engine speed does not exceed 2500-3000 RPM. You should note a change of at least 18 PSI, perhaps more depending on the vehicle manufacturer and the vehicle’s model year.

If that is okay, with a DVOM, check that you have 5V on the exhaust pressure sensor signal circuit (red lead to the sensor’s positive circuit, black lead to a good ground). If there is no 5 volts at the sensor, or if you see 12 volts at the sensor, repair the wiring from the PCM to the sensor, or again a faulty PCM.

If that is okay, check that the exhaust pressure sensor is properly grounded. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the exhaust pressure sensor circuit ground. If the test light does not illuminate, this would indicate a circuit problem. If it lights up, wiggle the wire harness going to each terminal to see if the test light flickers, indicating an intermittent connection.

If all tests have been successful so far and you continue to get a P04A3 code, try wiggling the sensor’s wire harness while watching the scan tool to see if the code returns. If it does, this most likely indicates an intermittent connection in the harness. If it does not, this would most likely indicate a faulty exhaust pressure sensor, although a closed exhaust pressure control valve or a faulty PCM cannot be ruled out until the sensor has been replaced.

P04A4 Exhaust Pressure Control Valve B Stuck Open

Exhaust Pressure Control Valve B Stuck Open

What Does It Mean?

This is a generic diagnostic trouble code (DTC) for the powertrain and generally applies to OBD-II equipped vehicles. This may include, but is not limited to, vehicles from Dodge, Honda, Chevy, Ford, VW, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

A stored code P04A4 means that the Powertrain Control Module (PCM) has detected a malfunction in one of the exhaust pressure control valves (regulator). The “B” valve typically indicates that the issue occurred in the engine bank that does not contain cylinder number one, but designs vary by manufacturer. In this case, the valve appears to be stuck in the open position.

Exhaust pressure regulators (also called back-pressure) are used in turbocharged gasoline and diesel engines. The operation of the exhaust back-pressure control valve is often similar to that of a throttle body. It uses an electronically controlled plate to restrict exhaust flow as determined by the PCM. There is also an exhaust back-pressure control valve position sensor and/or an exhaust back-pressure sensor.

Increased exhaust back-pressure is used to raise engine and coolant temperature more quickly. This can be particularly useful in very cold climates.

This is a basic generic overview of how the exhaust pressure group valve operates. Check the specifications of the vehicle in question before making assumptions. When the PCM detects a cold air intake temperature below a minimum threshold, it initiates the operation of the exhaust back-pressure valve and maintains it until the intake air temperature normalizes. The activation of the exhaust back-pressure regulator typically only occurs once per ignition cycle. The exhaust back-pressure control valve is designed to park in the wide-open position once it is deactivated by the PCM.

If the PCM detects that the exhaust back-pressure regulator is not in the desired position, or if the exhaust back-pressure sensor indicates it is out of position, a P04A4 code will be stored and a Malfunction Indicator Light (MIL) may illuminate.
How Severe Is This DTC?

Since exhaust back-pressure can affect climate control and driving functions, a stored P04A4 code should be addressed with a certain degree of urgency.
What Are Some of the Symptoms of the Code?

Symptoms of a P04A4 trouble code may include:

Delayed engine warm-up
Engine stalling or stumbling when cold
Reduced cold engine performance
Other exhaust back-pressure codes

What Are Some Common Causes of the Code?

Causes

of this P04A4 code may include:

Faulty exhaust back-pressure control valve position sensor
Bad exhaust pressure sensor
Defective exhaust pressure control valve
Open or shorted wiring in any of the exhaust pressure control valve circuits

What Are the P04A4 Troubleshooting Steps?

A reliable source of vehicle information will be needed to diagnose a P04A4 code. Other necessary tools:

A diagnostic scanner
A digital volt/ohmmeter (DVOM)
An infrared thermometer with a laser pointer

After a careful visual inspection of the wiring and connectors related to the system, locate the vehicle’s diagnostic port. Connect the scanner to the port and retrieve all stored codes and freeze frame data. Note this information, as it may be useful during your diagnosis.

Now, clear the codes and test-drive the vehicle to see if the P04A4 returns immediately. If there are intake air temperature codes or engine coolant temperature codes, diagnose and repair them before attempting to diagnose the P04A4.

Look for Technical Service Bulletins (TSBs) that apply to the vehicle, the codes, and the symptoms in question. If you find one that matches, it will likely help you greatly in your diagnosis.

If no obvious wiring or connector issues are discovered, start by testing the expected voltage signal at the exhaust pressure control valve (with the DVOM). You may need to use the scanner to simulate a cold start condition and activate the exhaust pressure control system.
If the proper voltage/ground signal is not detected at the exhaust pressure control valve connector, disconnect all associated controllers and use the DVOM to test the resistance and continuity of the individual circuit. Circuits found to be out of specification must be repaired or replaced.
If the correct degree of voltage/ground is found at the exhaust pressure control valve, follow the manufacturer’s recommendations for testing the exhaust pressure control valve (using the DVOM). If the exhaust pressure control valve pinout test does not match the manufacturer’s specifications, it must be replaced.
If the exhaust pressure control valve and circuits are functioning, test the exhaust pressure control valve position sensor or the exhaust pressure sensor (as applicable) according to the manufacturer’s specifications. Replace faulty components as necessary.

P04A5 Exhaust Pressure Control Valve B Stuck Closed

What does it mean?

This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II equipped vehicles. This may include, but is not limited to, Dodge, Honda, Chevy, Ford, VW, etc. vehicles. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.

A stored P04A5 code means that the Powertrain Control Module (PCM) has detected a malfunction in one of the exhaust pressure control valves (regulator). The “B” valve typically indicates that the problem occurred in the engine bank that does not contain cylinder number one, but designs vary by manufacturer. In this case, the valve appears to be stuck in the closed position.

Increased exhaust back-pressure is used to raise engine and coolant temperature more quickly. This can be particularly useful in very cold climates.

If the PCM detects that the exhaust back-pressure regulator is not in the desired position, or if the exhaust back-pressure sensor indicates it is out of position, a P04A5 code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated.
How severe is this DTC?

Since exhaust back-pressure can affect climate control and driving functions, a stored P04A5 code should be treated with a certain degree of urgency.
What are some of the symptoms of the code?

Symptoms of a P04A5 trouble code may include:

Severely decreased engine performance
Engine or transmission overheating
Exhaust may glow red after driving
Other exhaust back-pressure codes

What are some of the common causes of the code?

Causes

of this P04A5 code may include:

What are the troubleshooting steps for P04A5?

A reliable source of vehicle information will be necessary to diagnose a P04A5 code. Other necessary tools:

A diagnostic scanner
A digital volt/ohmmeter (DVOM)
An infrared thermometer with a laser pointer

Now, clear the codes and test-drive the vehicle to see if the P04A5 returns immediately. If there are any intake air temperature codes or engine coolant temperature codes, diagnose and repair them before attempting to diagnose the P04A5.

Look for Technical Service Bulletins (TSBs) that apply to the vehicle, the codes, and the symptoms in question. If you find one that matches, it will likely help you greatly in your diagnosis.

If no obvious wiring or connector issues are discovered, start by testing the expected voltage signal at the exhaust pressure control valve (using the DVOM). You may need to use the scanner to simulate a cold start condition and activate the exhaust pressure control system.
If the proper voltage/ground signal is not detected at the exhaust pressure control valve connector, disconnect all associated controllers and use the DVOM to test the resistance and continuity of the individual circuit. Circuits found to be non-compliant must be repaired or replaced.
If the correct degree of voltage/ground is found at the exhaust pressure control valve, follow the manufacturer’s recommendations for testing the exhaust pressure control valve (using the DVOM). If the exhaust pressure control valve pinout test does not match the manufacturer’s specifications, it must be replaced.
If the exhaust pressure control valve and circuits are operational, test the exhaust pressure control valve position sensor or the exhaust pressure sensor (as applicable) according to the manufacturer’s specifications. Replace faulty components as necessary.

You can use the infrared thermometer to get an actual reading of the exhaust temperature if no scanner data display is available. This could prove useful in determining whether the exhaust pressure control valve is actually operating or not. It can also detect a valve stuck in the open or closed position.

Under certain circumstances, a faulty catalytic converter or muffler will not cause a P04A5 code to be stored
Exhaust pressure control systems are most often used in turbocharged/supercharged applications