Catalytic Converter Heater Control Circuit (Bank 2)

What does it mean?

This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles (BMW, Honda, Mitsubishi, Toyota, Ford, Jeep, Hyundai, etc.). Although generic, the specific repair steps may vary by make/model.

If you are faced with diagnosing a stored P0439 code, you should know that it means the Powertrain Control Module (PCM) has detected a problem with the heated catalyst control circuit for engine bank two. Bank 2 specifies that the malfunction occurred in the catalytic converter for the engine bank that does not contain cylinder number one. Conditions that can lead to this code being stored can be electrical or mechanical.

The main function of the heated catalytic converter is to reduce exhaust emissions from diesel and gasoline engines. It is a dense ceramic fiber and precious metal filtration element enclosed in a steel housing and positioned in the exhaust pipe. Harmful nitrogen oxides (N2O), carbon monoxide, and unburned hydrocarbons are all converted into harmless nitrogen, oxygen, carbon dioxide, and water ions after passing through the heated catalytic converter. This is accomplished using the filtration element and the extreme heat from the engine exhaust.

In the case of the heated catalytic converter, the filtration element is further heated with a PCM-controlled injection of a certain type of flammable diesel exhaust fluid. Catalytic converter temperatures must reach at least 800 degrees Fahrenheit, and heated catalyst units can reach 1,200 degrees Fahrenheit.

The efficiency of the catalytic converter is monitored using upstream and downstream oxygen (O2) sensors and exhaust temperature sensors.

If the heated catalyst is not functioning correctly, the variations in oxygen concentration between the input exhaust and the output exhaust will not be significant. If the upstream and downstream O2 sensors reflect a similar exhaust oxygen concentration, or if an electrical malfunction is detected in the heated catalyst control circuit, a P0439 code will be stored and a malfunction indicator lamp may illuminate.

Other catalyst efficiency trouble codes for bank 2 include:

P0430 Catalyst System Efficiency Below Threshold (Bank 2)
P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2)
P0432 Main Catalyst Efficiency Below Threshold (Bank 2)
P0433 Heated Catalyst Efficiency Below Threshold (Bank 2)
P0434 Heated Catalyst Temperature Below Threshold (Bank 2)
P0435, P0436, P0437, P0438 Catalyst Temperature Sensor Circuit Codes

Code Severity and Symptoms

Since the catalyst heater is crucial for reducing exhaust emissions, a P0439 code should be considered severe.

Symptoms of this code may include:

Decreased fuel efficiency
A lack of overall engine performance
Excessive black smoke from the exhaust
Other associated diagnostic trouble codes
MIL (Malfunction Indicator Lamp) illumination

Causes

Possible causes for this code being set are as follows:

Faulty exhaust temperature sensor
Incorrect or insufficient diesel exhaust fluid
Faulty diesel exhaust fluid injection system
Burned, chafed, broken, or disconnected wiring and/or connectors
Faulty O2 sensor(s)
Faulty catalytic converter
Engine exhaust leak

Diagnostic and Repair Procedures

For me, a diagnostic scanner, a digital volt ohmmeter (DVOM), an infrared thermometer (with a laser pointer), and a reliable source of vehicle information (like All Data DIY) will be necessary when diagnosing a P0439 code.

All diesel exhaust fluid injection codes, misfire codes, throttle position sensor codes, manifold air pressure codes, and mass air flow sensor codes should be addressed before attempting to diagnose a stored P0439 code. The engine must be in good working order before diagnosing this code.

I usually start my diagnosis with a visual inspection of the system’s wiring harnesses and connectors. I would focus my attention on harnesses routed near hot exhaust pipes and manifolds, as well as those routed near sharp edges like those found on exhaust shields.

Next, I would connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes and freeze frame data. I write this information down as it can be helpful if this turns out to be an intermittent code. Clear the codes and test drive the vehicle to see if the P0439 resets.

If applicable, ensure the diesel exhaust fluid tank is filled with the correct fluid and that the injection system is operating correctly. If the diesel exhaust fluid injection system fails, the heated catalyst will not function efficiently and a P0439 code will be stored. If the diesel exhaust fluid injection system is not operating correctly, check the system fuses and relays to ensure the controller is functioning.

If the diesel exhaust fluid injection system is operating as expected, use the infrared thermometer to test the inlet and outlet temperatures of the catalytic converter. Use the vehicle information source and compare the actual temperature data with the manufacturer’s specifications. If the outlet temperature does not meet specifications, suspect a faulty catalytic converter.

If the heated catalyst outlet temperature meets specifications, use the DVOM to test the exhaust temperature sensor using the specifications found in the vehicle information source. Replace the exhaust temperature sensor if it does not meet the manufacturer’s specifications.

Test the O2 sensors following the manufacturer’s recommendations.

Additional diagnostic notes:

P0439 code is frequently stored due to incorrect or insufficient diesel exhaust fluid
Disconnect associated controllers before probing circuits with the DVOM

P043A Catalyst Temperature Sensor Circuit Malfunction, Bank 2 Sensor 2

What Does It Mean?

This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles that have a catalytic converter temperature sensor (Subaru, Ford, Chevy, Jeep, Nissan, Mercedes-Benz, Toyota, Dodge, etc.). Although generic, the exact repair steps may vary by make/model.

The catalytic converter is one of the most important emission devices on a vehicle. Exhaust gases pass through the catalytic converter where a chemical reaction occurs. This reaction transforms carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into harmless water (H2O) and carbon dioxide (CO2).

The converter’s efficiency is monitored by two oxygen sensors; one mounted upstream of the converter and one mounted downstream. By comparing the oxygen sensor (O2) signals, the powertrain control module (PCM) can determine if the catalytic converter is functioning properly. A standard zirconia pre-catalyst O2 sensor will rapidly switch its output signal between approximately 0.1 and 0.9 volts. A reading of 0.1 volt indicates a lean air/fuel mixture, while 0.9 volt indicates a rich mixture. If the converter is working correctly, the downstream sensor should settle steadily around 0.45 volts.

The catalytic converter’s efficiency and temperature go hand in hand. If the converter is operating as it should, the outlet temperature should be slightly higher than the inlet. The old rule of thumb was a 100-degree Fahrenheit difference. However, many modern vehicles might not show that much difference.

There is no actual “catalyst temperature sensor.” What the codes described in this article refer to is the oxygen sensor. The “Bank 2” part of the code indicates the problem is coming from the engine’s second bank. That is, the bank that does not include cylinder number 1. “Sensor 2” refers to the sensor mounted downstream of the catalytic converter.

Fault code P043A is set when the PCM detects a malfunction in the Bank 2 Sensor 2 catalyst temperature circuit.
Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P043A engine code may include:

Check Engine Light illuminated
Poor engine performance
Reduced fuel economy
Increased emissions

Causes

Possible causes of this P043A code include:

Faulty oxygen sensor
Wiring issues
Unbalanced air/fuel mixture
PCM programming / Faulty PCM

Diagnostic and Repair Procedures

Start by visually inspecting the downstream oxygen sensor and its corresponding wiring. Look for loose connections, damaged wiring, etc. Also check for exhaust leaks visually and audibly. An exhaust leak can cause a false oxygen sensor code. If damage is found, repair as needed, clear the code, and see if it returns.

Next, check for Technical Service Bulletins (TSBs) regarding the issue. If nothing is found, you will need to move on to step-by-step diagnosis of the system. The following is a generalized procedure, as tests for this code vary by vehicle. To accurately test the system, you will need to refer to a diagnostic flowchart specific to the vehicle’s make/model.
Check for Other DTCs

Oxygen sensor codes can often be set due to engine performance issues causing an unbalanced air/fuel mixture. If other fault codes are stored, you should address those first before proceeding with oxygen sensor diagnosis.
Check Sensor Operation

To do this, it’s best to use a scan tool or, even better, an oscilloscope. Since most individuals don’t have access to an oscilloscope, we will cover diagnosing the oxygen sensor using a scan tool. Connect the scan tool to the OBD port under the dashboard. Turn on the scan tool and choose the Bank 2 Sensor 2 voltage parameter from the data list. Bring the engine to operating temperature and view the sensor’s operation on the scan tool in graph mode.

The sensor should have a steady reading of 0.45 volts with only very small fluctuations. If it is not responding correctly, it will likely need to be replaced.
Check the Circuit

Oxygen sensors produce their own voltage signal which is sent back to the PCM. Before continuing, you will want to consult factory wiring diagrams to determine which wires are which. Autozone offers free online repair manuals for many vehicles and ALLDATADIY offers single-vehicle subscriptions. To check continuity between the sensor and the PCM, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (ignition off) between the PCM’s O2 sensor signal terminal and the signal wire. If the meter reads Out of Limits (OL), there is an open circuit between the PCM and the sensor which will need to be located and repaired. If the meter reads a numerical value, there is continuity.

Next, you will want to check the ground side of the circuit. To do this, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a multimeter set to ohms (ignition off) between the O2 sensor connector ground terminal (harness side) and chassis ground. If the meter reads Out of Limits (OL), there is an open circuit on the ground side of the circuit which will need to be located and repaired. If the meter reads a numerical value, there is ground continuity.

Finally, you will want to verify that the PCM is processing the O2 sensor signal correctly. To do this, leave all connectors connected and insert a back-probing pin into the PCM’s signal terminal. Set the digital multimeter to the DC volts setting. With the engine warmed up, compare the voltage reading on the meter to the one on the scan tool. If the two do not match, the PCM is likely faulty or requires reprogramming.

P043B Catalyst Temperature Sensor Circuit Range/Performance B2S2

What Does It Mean?

The converter’s efficiency is monitored by two oxygen sensors; one mounted upstream of the converter and one mounted downstream. By comparing the oxygen sensor (O2) signals, the powertrain control module (PCM) can determine whether the catalytic converter is functioning properly. A standard zirconia pre-catalyst O2 sensor will rapidly switch its output signal between approximately 0.1 and 0.9 volts. A reading of 0.1 volt indicates a lean air/fuel mixture, while 0.9 volt indicates a rich mixture. If the converter is working correctly, the downstream sensor should settle steadily around 0.45 volts.

The catalytic converter’s efficiency and temperature go hand in hand. If the converter is functioning as it should, the outlet temperature should be slightly higher than the inlet. The old rule of thumb was a 100-degree Fahrenheit difference. However, many modern vehicles might not show that much difference.

Diagnostic trouble code P043B is set when the PCM detects a problem with the range or performance in the Bank 2 Sensor 2 catalyst temperature circuit.
Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P043B engine code may include:

Check Engine Light illuminated
Poor engine performance
Reduced fuel economy
Increased emissions

Causes

Possible causes of this P043B code include:

Faulty oxygen sensor
Wiring issues
Unbalanced air/fuel mixture
PCM programming / Faulty PCM

Diagnostic and Repair Procedures

Oxygen sensor codes can often be set due to engine performance issues causing an unbalanced air/fuel mixture. If other trouble codes are stored, you should address those first before proceeding with oxygen sensor diagnosis.
Check Sensor Operation

The sensor should have a steady reading of 0.45 volts with only very small fluctuations. If it is not responding correctly, it will likely need to be replaced.
Check the Circuit

Oxygen sensors produce their own voltage signal which is sent back to the PCM. Before continuing, you will need to consult factory wiring diagrams to determine which wires are which. Autozone offers free online repair manuals for many vehicles and ALLDATADIY offers single-vehicle subscriptions. To check continuity between the sensor and the PCM, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (ignition off) between the PCM’s O2 sensor signal terminal and the signal wire. If the meter reads Out of Limits (OL), there is an open circuit between the PCM and the sensor that will need to be located and repaired. If the meter reads a numerical value, there is continuity.

Next, you will want to check the ground side of the circuit. To do this, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (ignition off) between the O2 sensor connector ground terminal (harness side) and chassis ground. If the meter reads Out of Limits (OL), there is an open circuit on the ground side of the circuit that will need to be located and repaired. If the meter reads a numerical value, there is continuity to ground.

Finally, you will want to verify that the PCM is processing the O2 sensor signal correctly. To do this, leave all connectors connected and insert a back-probing pin into the PCM’s signal terminal. Set the digital multimeter to the DC volts setting. With the engine warmed up, compare the voltage reading on the meter to that on the scan tool. If the two do not match, the PCM is likely faulty or requires reprogramming.

P043C Low Catalyst Temperature Sensor Circuit B2S2

What Does It Mean?

The catalytic converter is one of the most important emission control devices on a vehicle. Exhaust gases pass through the catalytic converter where a chemical reaction occurs. This reaction transforms carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into harmless water (H2O) and carbon dioxide (CO2).

The converter’s efficiency is monitored by two oxygen sensors; one mounted upstream of the converter and one mounted downstream. By comparing the signals from the oxygen (O2) sensors, the Powertrain Control Module (PCM) can determine if the catalytic converter is functioning correctly. A standard zirconia pre-catalyst O2 sensor will rapidly switch its output signal between approximately 0.1 and 0.9 volts. A reading of 0.1 volt indicates a lean air/fuel mixture, while 0.9 volts indicates a rich mixture. If the converter is working properly, the downstream sensor should settle steadily around 0.45 volts.

The catalytic converter’s efficiency and temperature go hand in hand. If the converter is operating as it should, the outlet temperature should be slightly higher than the inlet temperature. The old rule of thumb was a 100-degree Fahrenheit difference. However, many modern vehicles might not show that much of a difference.

There is no actual “catalyst temperature sensor.” What the codes described in this article refer to is the oxygen sensor. The “Bank 2” part of the code indicates the problem is coming from the engine’s second bank. That is, the bank which does not include cylinder number 1. “Sensor 2” refers to the sensor mounted downstream of the catalytic converter.

Fault code P043C is set when the PCM detects a low catalyst temperature sensor signal in the Bank 2 Sensor 2 catalyst temperature circuit. This typically indicates the circuit is shorted.
Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P043C engine code may include:

Check Engine Light illuminated
Poor engine performance
Reduced fuel economy
Increased emissions

Causes

Possible causes of this P043C code include:

Faulty oxygen sensor
Wiring issues
Unbalanced air/fuel mixture
PCM programming / Faulty PCM

Diagnostic and Repair Procedures

Next, check for Technical Service Bulletins (TSBs) regarding the issue. If nothing is found, you will need to proceed with step-by-step diagnosis of the system. The following is a generalized procedure, as tests for this code vary by vehicle. To accurately test the system, you will need to refer to a diagnostic flowchart specific to the vehicle’s make/model.
Check for Other DTCs

To do this, it’s best to use a scan tool or, even better, an oscilloscope. Since most individuals do not have access to an oscilloscope, we will cover diagnosing the oxygen sensor using a scan tool. Connect the scan tool to the OBD port under the dashboard. Turn on the scan tool and choose the Bank 2 Sensor 2 voltage parameter from the data list. Bring the engine to operating temperature and view the sensor’s operation on the scan tool in graph mode.

The sensor should have a steady reading of 0.45 volts with only very small fluctuations. If it is not responding correctly, it will likely need to be replaced.
Check the Circuit

Oxygen sensors produce their own voltage signal which is sent back to the PCM. Before continuing, you will want to consult factory wiring diagrams to determine which wires are which. Autozone offers free online repair manuals for many vehicles and ALLDATADIY offers single-vehicle subscriptions. To check for continuity between the sensor and the PCM, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (power off) between the PCM’s O2 sensor signal terminal and the signal wire. If the meter reads Out of Limits (OL), there is an open circuit between the PCM and the sensor which will need to be located and repaired. If the meter reads a numerical value, there is continuity.

Next, you will want to check the ground side of the circuit. To do this, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (power off) between the O2 sensor connector ground terminal (harness side) and chassis ground. If the meter reads Out of Limits (OL), there is an open circuit on the ground side of the circuit which will need to be located and repaired. If the meter reads a numerical value, there is ground continuity.

P043D Catalyst Temperature Sensor B2S2 High Circuit

What does it mean?

This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles that have a catalyst temperature sensor (Subaru, Ford, Chevy, Jeep, Nissan, Mercedes-Benz, Toyota, Dodge, etc.). Although generic, the specific repair steps may vary by make/model.

The catalytic converter is one of the most important emission devices on a vehicle. Exhaust gases pass through the catalytic converter where a chemical reaction occurs. This reaction converts carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into harmless water (H2O) and carbon dioxide (CO2).

The converter’s efficiency is monitored by two oxygen sensors; one mounted upstream of the converter and one mounted downstream. By comparing the signals from the oxygen (O2) sensors, the powertrain control module (PCM) can determine if the catalytic converter is functioning properly. A standard zirconia pre-catalyst O2 sensor will rapidly switch its output signal between approximately 0.1 and 0.9 volts. A reading of 0.1 volt indicates a lean air/fuel mixture, while 0.9 volt indicates a rich mixture. If the converter is working correctly, the downstream sensor should read steadily around 0.45 volts.

There is no actual “catalyst temperature sensor.” What the codes in this article refer to is the oxygen sensor. The “bank 2” part of the code indicates the issue is from the engine’s second bank. That is, the bank that does not include cylinder number 1. “Sensor 2” refers to the sensor mounted downstream of the catalytic converter.

Trouble code P043D is set when the PCM detects a high catalyst temperature sensor signal in bank 2, catalyst temperature sensor 2 circuit. This typically indicates an open circuit.

Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P043D engine code may include:

Check Engine Light illuminated
Poor engine performance
Reduced fuel economy
Increased emissions

Causes

Possible causes of this P043D code include:

Faulty oxygen sensor
Wiring issues
Unbalanced air/fuel mixture
PCM programming / faulty PCM

Diagnostic and Repair Procedures

Start by visually inspecting the downstream oxygen sensor and its associated wiring. Look for loose connections, damaged wiring, etc. Also check for exhaust leaks visually and audibly. An exhaust leak can cause a false oxygen sensor code. If damage is found, repair as necessary, clear the code, and see if it returns.

Next, check for Technical Service Bulletins (TSBs) regarding the issue. If nothing is found, you’ll need to move on to step-by-step diagnosis of the system. The following is a generalized procedure, as tests for this code vary by vehicle. To accurately test the system, you will need to refer to a diagnostic flowchart specific to the vehicle’s make/model.
Check for Other DTCs

The sensor should have a steady reading of 0.45 volts with only very small fluctuations. If it does not respond correctly, it will likely need to be replaced.
Check the Circuit

Oxygen sensors produce their own voltage signal that is sent back to the PCM. Before proceeding, you’ll want to consult factory wiring diagrams to determine which wires are which. Autozone offers free online repair manuals for many vehicles, and ALLDATADIY offers single-vehicle subscriptions. To check continuity between the sensor and the PCM, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (power off) between the PCM’s O2 sensor signal terminal and the signal wire. If the meter reads out of limits (OL), there is an open circuit between the PCM and the sensor that will need to be located and repaired. If the meter reads a numerical value, there is continuity.

Next, you’ll want to check the ground side of the circuit. To do this, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (power off) between the O2 sensor connector ground terminal (harness side) and chassis ground. If the meter reads out of limits (OL), there is an open circuit on the ground side of the circuit that will need to be located and repaired. If the meter reads a numerical value, there is continuity to ground.

Finally, you’ll want to verify that the PCM is processing the O2 sensor signal correctly. To do this, leave all connectors connected and insert a back-probing pin into the PCM’s signal terminal. Set the digital multimeter to the DC volts setting. With the engine warmed up, compare the voltage reading on the meter to that on the scan tool. If the two do not match, the PCM is likely faulty or requires reprogramming.

P043E Evaporative Emission System Reference Orifice Low Flow Leak Detection

What does it mean?

This is a generic diagnostic trouble code (DTC) that generally applies to OBD-II vehicles with an EVAP system that uses a leak detection system. This may include, but is not limited to, vehicles from Toyota, Scion, GM, Chevrolet, Hyundai, Pontiac, Volvo, etc. Anecdotally, this code appears to be much more common on Toyota-brand vehicles. Although generic, the exact repair steps may vary by year, make, model, and powertrain configuration.
The PCM has detected an anomaly in the leak detection reference orifice of the Evaporative Emission (EVAP) system when a P043E code is stored in your OBD-II vehicle. In this case, a low flow condition has been indicated.

The EVAP system is designed to capture fuel vapors (from the fuel tank) before they escape into the atmosphere. The EVAP system uses a vented reservoir (commonly called a canister) to store excess vapors until the engine is operating under the right conditions to burn them as efficiently as possible.

The pressure (developed when fuel is stored) acts as the propellant, causing the vapors to leak through the tubes and eventually into the canister. A charcoal element, contained in the canister, absorbs the fuel vapors and holds them for release at the appropriate time.

An assortment of sample orifices, a leak detection pump, a charcoal canister, the EVAP pressure sensor, the purge valve/solenoid, the vent control valve/solenoid, and a complex system of metal tubes and rubber hoses (extending from the fuel tank to the engine compartment) are typical components of the EVAP system.

Engine vacuum is used by the EVAP system to draw fuel vapors (from the charcoal canister and through the lines) into the intake manifold where they can be burned instead of being released into the atmosphere. The PCM electronically controls the purge control valve/solenoid, which is the gateway of the EVAP system. It is responsible for regulating the intake vacuum in the EVAP canister so that fuel vapors can be drawn into the engine only when conditions are ideal for the fuel pressure vapors to be burned as efficiently as possible.

Some EVAP systems use an electronic leak detection pump to increase pressure in the system, so that the system can be tested for leaks/flow. Leak detection reference orifices may be placed at a single point or at multiple points throughout the EVAP system. Leak detection reference orifices are typically of the inline variety so that a precise degree of flow can be measured with the leak detection pump activated. The PCM uses input signals from the EVAP pressure and flow sensors, in conjunction with the leak detection reference orifice(s), to determine if the leak detection system is functioning properly. The EVAP leak detection reference orifice may be a small filter-like device or simply an area of the EVAP line that restricts flow so that an EVAP pressure/flow sensor gets an accurate sample.

If the PCM detects a low flow condition through the EVAP leak detection reference orifice, a P043E code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated.

How severe is this DTC?

EVAP leak detection codes, similar to P043E, pertain exclusively to the evaporative emission control system and should not be classified as severe.
What are some of the symptoms of the code?

Symptoms of a P043E trouble code will most likely result in few or no visible symptoms. You may see slightly decreased fuel economy and other EVAP leak detection diagnostic codes.
What are some of the common causes of the code?

Causes

of this P043E engine code may include:

Faulty EVAP pressure sensor
A damaged or clogged EVAP leak detection orifice
Broken charcoal element (canister)
Cracked or crushed EVAP or vacuum line(s)
Faulty vent control or purge control solenoid
Bad leak detection pump

What are the P043E troubleshooting steps?

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information will prove necessary to diagnose a P043E code.

Use your vehicle information source to check for Technical Service Bulletins (TSBs) that match the symptoms and codes present in the diagnosed vehicle. If you can find the appropriate TSB, it will likely direct you to the exact source of the malfunction without costing you much time and trouble.

If other EVAP system codes are present, diagnose and repair them before attempting to diagnose P043E. P043E could be in response to conditions that caused other EVAP codes.

Before getting your hands dirty, connect the scanner to the vehicle’s diagnostic port and retrieve all stored codes and freeze frame data. I like to note this information as it may be useful as my diagnosis progresses. After that, clear the codes and test drive the vehicle to see if the code resets.

Ideally, you want to test drive the vehicle until one of two things happens; the PCM enters readiness mode or the code resets. If the PCM enters readiness mode, you have an intermittent problem (or you inadvertently fixed it) and there’s not much you can do now. If it comes back later, the failure condition may have worsened and you can start over. If the P043E resets, you know you have a hard and fast malfunction and it’s time to dig in and find it.

Start with a visual inspection of all wiring harnesses and connectors related to the EVAP system that you can reasonably access. Obviously, you’re not going to remove major components to take a look, but focus your efforts on high-temperature areas and areas where wiring, connectors, vacuum lines, and vapor hoses may interfere with moving components. Many cars are repaired during this phase of the diagnostic process, so focus and put some effort into it.

Connect the scanner to the vehicle’s diagnostic port and observe the data stream. EVAP flow and pressure data should conform to the manufacturer’s specifications when the system is activated. In most cases, activating the EVAP system (purge control solenoid and/or leak detection pump) may be possible using the scanner. Some EVAP sensor testing will need to be done with the system activated.

Use the DVOM to test the EVAP sensors and solenoids to compare them with the manufacturer’s specifications. All related components that do not meet specifications will need to be replaced. If possible, access the EVAP leak detection reference orifice to check for charcoal contamination. If charcoal contamination is detected, suspect that the EVAP canister has been compromised.

Before testing system circuits with the DVOM, disconnect all associated controllers to prevent damage. Test the appropriate levels of resistance and continuity between individual EVAP components and the PCM using the DVOM. Circuits that do not meet specifications will need to be repaired or replaced.

A loose or faulty fuel cap will not cause a P043E code to be stored
This code is applicable only to vehicle EVAP systems that use a leak detection system

P043F Evaporation Flow Rate System Leak Detection High Flow Reference Orifice

What does it mean?

The PCM has detected an anomaly in the evaporative emission (EVAP) system leak detection reference orifice when a P043F code is stored in your OBD-II vehicle. In this case, a high flow condition was indicated.

The EVAP system is designed to capture fuel vapors (from the fuel tank) before they escape into the atmosphere. The EVAP system uses a vented reservoir (commonly called a canister) to store excess vapors until the engine is operating under the proper conditions to burn them as efficiently as possible.

The pressure (developed when fuel is stored) acts as the propellant, causing the vapors to leak through the tubes and eventually into the canister. A charcoal element, contained within the canister, absorbs the fuel vapors and holds them for timely release.

An assortment of sample orifices, a leak detection pump, a charcoal canister, the EVAP pressure sensor, the purge valve/solenoid, the vent control valve/solenoid, and a complex system of metal lines and rubber hoses (extending from the fuel tank to the engine compartment) are typical components of the EVAP system.

Engine vacuum is used by the EVAP system to draw fuel vapors (from the charcoal canister and through the lines) into the intake manifold where they can be burned instead of being released into the atmosphere. The PCM electronically controls the purge control valve/solenoid which is the gateway of the EVAP system. It is responsible for regulating the intake vacuum in the EVAP canister so that fuel vapors can be drawn into the engine only when conditions are ideal for the fuel pressure vapors to be burned as efficiently as possible.

Some EVAP systems use an electronic leak detection pump to increase pressure within the system, so the system can be tested for leaks/flow. Leak detection reference orifices may be placed at a single point or at multiple points throughout the EVAP system. Leak detection reference orifices are typically of the inline variety so that a precise degree of flow can be measured with the leak detection pump activated. The PCM uses input signals from EVAP pressure and flow sensors, in conjunction with the leak detection reference orifice(s), to determine if the leak detection system is functioning properly. The EVAP leak detection reference orifice may be a small filter-like device or simply an area of the EVAP line that restricts flow so that an EVAP pressure/flow sensor obtains an accurate sample.

If the PCM detects a high flow condition through the EVAP leak detection reference orifice, a P043F code will be stored and a malfunction indicator lamp (MIL) may illuminate.
How severe is this DTC?

EVAP leak detection codes, similar to P043F, pertain exclusively to the evaporative emission control system and should not be classified as severe.
What are some of the symptoms of the code?

Symptoms of a P043F trouble code may include:

No symptoms are likely to be manifested
Hissing or humming (even when the ignition is off)
Slightly decreased fuel efficiency
Other EVAP leak detection codes may be stored

What are some common causes of the code?

Causes

of this P043F engine code may include:

Faulty EVAP pressure sensor
Faulty vent control or purge control solenoid
Faulty leak detection pump

What are the troubleshooting steps for P043F?

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information will prove necessary to diagnose a P043F code.

Use your vehicle information source to check for technical service bulletins (TSBs) that match the symptoms and codes present in the diagnosed vehicle. If you can find the appropriate TSB, it will likely direct you to the exact source of the malfunction without costing you much time and trouble.

If other EVAP system codes are present, diagnose and repair them before attempting to diagnose P043F. P043F could be in response to conditions that caused other EVAP codes.

Before getting your hands dirty, connect the scanner to the vehicle’s diagnostic port and retrieve all stored codes and freeze frame data. I like to note this information as it can be helpful as my diagnosis progresses. After that, clear the codes and test drive the vehicle to see if the code resets.

Ideally, you would want to test drive the vehicle until two things happen; the PCM enters readiness mode or the code resets. If the PCM enters readiness mode, you have an intermittent problem (or you inadvertently fixed it) and you can’t do much about it now. If it comes back later, the failure condition may have worsened and you can start over. If P043F resets, you know you have a hard and fast malfunction and it’s time to dig in and find it.

Connect the scanner to the vehicle’s diagnostic port and observe the data stream. EVAP flow and pressure data should conform to manufacturer specifications when the system is activated. In most cases, activating the EVAP system (purge control solenoid and/or leak detection pump) may be possible using the scanner. Some EVAP sensor testing will need to be performed with the system activated.

Use the DVOM to test EVAP sensors and solenoids, comparing them to manufacturer specifications. All related components that do not meet specifications will need to be replaced. If possible, access the EVAP leak detection reference orifice to check for charcoal contamination. If charcoal contamination is detected, suspect that the EVAP canister has been compromised.

Before testing system circuits with the DVOM, disconnect all associated controllers to prevent damage. Test for proper resistance and continuity levels between individual EVAP components and the PCM using the DVOM. Circuits that do not meet specifications will need to be repaired or replaced.

A loose or faulty fuel cap will not cause a P043F code to be stored
This code is applicable only to vehicle EVAP systems that use a leak detection system

P0440 Evaporative Emission Control System Malfunction

What does it mean?

This diagnostic code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.

It indicates that a part of the EVAP control system is no longer functioning properly. The EVAP system consists of many parts, including (but not limited to) the gas cap, fuel lines, carbon canister, purge valve, and other hoses.

The Evaporative Emission Control (EVAP) system prevents fuel vapors from escaping from a vehicle’s fuel system. Fuel vapors are routed through hoses to a charcoal canister for storage. Later, when the engine is running, a purge control valve opens, allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms

You will likely not notice any driving issues.

Causes

A P0440 code could mean that one or more of the following events have occurred:

The gas cap is not installed or is not working properly
The purge solenoid is faulty
The canister is clogged and not working properly

Possible Solutions

With an OBD-II P0440 trouble code, diagnosis can sometimes be difficult. Here are some tips to try:

Remove and reinstall the gas cap, clear the code, and drive for a day to see if the codes return.
Inspect the EVAP system for cuts/holes in the tubes/hoses
Inspect for damaged or disconnected hoses around the Evap purge solenoid
Check and/or replace the sensor
Check and/or replace the purge valve
Have a professional use a smoke machine to detect leaks

P0440 Repair Video

We are not affiliated with the producers of this diagnostic video, but we found it to be of excellent quality and worth sharing!

Other EVAP DTCs: P0441 – P0442 – P0443 – P0444 – P0445 – P0446 – P0447 – P0448 – P0449 – P0452 – P0453 – P0455 – P0456

P0441 Incorrect Purge Flow of Evaporative Emission Control System

Definition of Code P0441
Code P0441 is a generic powertrain code (OBD-II) related to the Evaporative Emission Control System (EVAP). It indicates a malfunction in the fuel vapor purge process, meaning the Powertrain Control Module (PCM) did not detect the expected flow when the purge was commanded.

EVAP System Operation
The EVAP system prevents fuel vapors from escaping into the atmosphere. It consists of:

Fuel tank cap
Fuel lines
Charcoal canister
Purge valve
Associated sensors and hoses

Vapors are stored in the charcoal canister and then purged into the engine via the purge valve, which is activated by intake vacuum. A vacuum switch checks the flow during this phase. If the PCM commands the purge but does not detect any flow (switch closed), code P0441 is triggered.

Common Symptoms

Illuminated Check Engine light (often the only visible symptom)
Possible slight increase in fuel consumption (rare)

Possible Causes

Electrical Problems: Open/short circuit in the purge solenoid, corroded connectors.
Mechanical Failures:
Faulty purge solenoid
Defective vacuum switch
Cracked EVAP lines or damaged canister
Restriction in the EVAP line or canister
PCM malfunction (rare)

Recommended Solutions

Basic Checks:

Check the fuel tank cap seal.
Inspect EVAP lines for cracks or disconnections.
Clean corroded connectors.

Specific Tests:

Test the purge solenoid’s resistance and power supply.
Check the operation of the vacuum switch.
Use a scanner to activate the purge and observe the flow.

Common Repairs:

Replace the purge solenoid (most common cause).
Repair damaged lines or the canister.
For Chrysler: replace the Leak Detection Pump (LDP).
In case of PCM failure: reprogram or replace the module.

Related EVAP DTC Codes

P0440 (Leak Detected) | P0442-P0449 (Valve/Calculation Malfunctions)
P0452/P0453 (Fuel Tank Pressure Sensor) | P0455/P0456 (Small/Large Leaks)

Note: Accurate diagnosis with an OBD-II tool and a smoke test is often necessary to locate the fault.

P0442 Evaporative Emission Control System Leak Detected (Small Leak)

Code P0442: Leak Detected in the EVAP System
Complete Guide to Understanding and Resolving the Issue

1. What is Code P0442?

Code P0442 is a generic OBD-II code related to the powertrain, indicating a minor leak in the Evaporative Emission Control (EVAP) system. It appears on many vehicles (Ford, GMC, Jeep, Dodge, Toyota, BMW, etc.), but repair steps may vary by make or model.

How the EVAP System Works

The EVAP system captures fuel vapors to prevent their release into the atmosphere:

Vapors are stored in an activated charcoal canister.
When the engine is running, a purge valve opens to burn these vapors in the engine.
The PCM (Powertrain Control Module) continuously monitors the system for leaks, even very small ones (starting from 0.04 inches in diameter).

2. Symptoms of Code P0442

Malfunction Indicator Lamp (MIL) illuminated (“Check Engine” light).
No noticeable impact on driving performance.
Occasionally: Fuel odor near the tank or engine.

3. Possible Causes

Fuel cap: Loose, damaged, or non-compliant (non-OEM part).
Leaks in lines/hoses: Cuts, cracks, or holes in the EVAP system.
Mechanical failures:
Worn vent O-ring.
Faulty purge or vent valve.
Failed leak detection pump.

4. Repair Solutions

Simple Steps (DIY)

Check the fuel cap:

Remove it, clean it, then reinstall it properly.
Clear the code with an OBD-II scanner and test the vehicle.
If the code returns, replace the cap with an OEM (Original Equipment Manufacturer) part.

Visual inspection:

Examine EVAP hoses and connections for cracks or disconnections.

Advanced Diagnostics

EVAP leak test: Use a diagnostic tool to activate the leak detection pump and measure pressure.
Smoke test: Identifies the exact location of leaks by injecting smoke into the system.
Component checks:
Test the purge valve with a multimeter.
Check the charcoal canister for leaks.

⚠️ Note: Exact procedures depend on the vehicle model. Consult a specific repair manual or a professional.

5. Related DTC Codes

Other common EVAP codes:
P0440, P0441, P0443, P0444, P0445, P0446, P0447, P0448, P0449, P0452, P0453, P0455, P0456.

6. Conclusion

Code P0442 indicates a minor leak, often related to the fuel cap or a damaged hose. While some repairs are DIY-friendly, a smoke test or mechanic’s intervention is recommended if the leak persists. Ignoring this code can lead to increased pollutant emissions and failure in emissions testing.