What does it mean?

This diagnostic code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles that have a catalytic 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 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 volts indicates a lean air/fuel mixture, while 0.9 volts indicates a rich mixture. If the converter is working properly, the downstream sensor should stabilize regularly around 0.45 volts.

The efficiency and temperature of the catalytic converter go hand in hand. If the converter is working 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 1” part of the code indicates that the problem is with the engine’s first bank. That is, the bank that includes cylinder number 1. “Sensor 1” refers to the sensor mounted upstream of the catalytic converter.

Trouble code P0428 is set when the PCM detects a catalyst temperature sensor signal. This typically indicates an open circuit.

Related diagnostic codes include:

• P0425 Catalyst Temperature Sensor Circuit Malfunction (Bank 1, Sensor 1)
• P0426 Catalyst Temperature Sensor Circuit Range/Performance (Bank 1, Sensor 1)
• P0427 Catalyst Temperature Sensor Circuit Low (Bank 1, Sensor 1)

Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P0428 engine code may include:

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

Causes

Possible causes of this P0428 code include:

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

Diagnostic and Repair Procedures

Start by visually inspecting the upstream 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 necessary, 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 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

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 them 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 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 1 Sensor 1 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 switch rapidly between rich and lean (0.1 volts and 0.9 volts). If the sensor’s response is slow, it is likely faulty and needs replacement.

If the sensor reads above 0.55 volts consistently, either the sensor is faulty, the air/fuel mixture is too rich, or there is an open in the sensor’s signal circuit. If the sensor reads below 0.35 volts consistently, either the sensor is faulty, the air/fuel mixture is too lean, or there is high resistance or a short in the signal wire to the PCM.

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 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-probe 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.

What does it mean?

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

If you’re facing diagnosis of a stored P0429 code, you should know this means the powertrain control module (PCM) has detected a problem with the catalytic converter heater control circuit for engine bank 1. The first bank indicates the malfunction occurred in the catalytic converter for the engine bank containing cylinder #1. Conditions that can cause this code to be stored may be electrical or mechanical.

The main function of the heated catalytic converter is to reduce exhaust emissions from diesel and gasoline engines. It’s a dense filtration element made of ceramic fibers and precious metals 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 catalytic converter’s efficiency is monitored using upstream and downstream oxygen sensors (O2) and exhaust temperature sensors.

If the heated catalyst isn’t functioning properly, the oxygen concentration variations between input and output exhaust won’t be significant. If the upstream and downstream O2 sensors reflect similar exhaust oxygen concentration, or if an electrical malfunction is detected in the heated catalyst control circuit, a P0429 code will be stored and a malfunction indicator light may illuminate.

Other bank 1 catalyst efficiency trouble codes include:

P0420 Catalyst System Efficiency Below Threshold (Bank 1)
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
P0423 Heated Catalyst Efficiency Below Threshold (Bank 1)
P0424 Heated Catalyst Temperature Below Threshold (Bank 1)
P0425, P0426, P0427, P0428 Catalyst Temperature Sensor Circuit Codes

Code Severity and Symptoms

Since the catalytic converter heater is crucial for exhaust emission reduction, a P0429 code should be considered severe.

Symptoms of this code may include:

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

Causes

Possible causes for setting this code are as follows:

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

Diagnostic and Repair Procedures

A diagnostic scanner, digital volt ohmmeter (DVOM), infrared thermometer (with laser pointer), and a reliable vehicle information source (like All Data DIY) will be needed when diagnosing a P0429 code.

All diesel exhaust fluid injection codes, misfire codes, throttle position sensor codes, manifold air pressure codes, and mass airflow sensor codes should be addressed before attempting to diagnose a stored P0429 code. The engine must be in good working condition before diagnosing this code.

I typically begin my diagnosis with a visual inspection of the system’s wiring harnesses and connectors. I would focus 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 down this information as it may prove helpful if this turns out to be an intermittent code. Clear the codes and test drive the vehicle to see if P0429 resets.

If applicable, ensure the diesel exhaust fluid tank is filled with the correct fluid and the injection system is functioning properly. If the diesel exhaust fluid injection system fails, the heated catalyst won’t function efficiently and a P0429 code will be stored. If the diesel exhaust fluid injection system isn’t working properly, check the system fuses and relays to ensure the controller is functioning.

If the diesel fluid injection system is working as expected, use the infrared thermometer to test the catalytic converter’s input and output temperatures. Use the vehicle information source and compare actual temperature data with manufacturer specifications. If the output temperature doesn’t meet specifications, suspect a faulty catalytic converter.

If the heated catalyst output temperature meets specifications, use the DVOM to test the exhaust temperature sensor using specifications found in the vehicle information source. Replace the exhaust temperature sensor if it doesn’t meet manufacturer specifications.

Test the O2 sensors following manufacturer recommendations.

Additional diagnostic notes:

P0429 code is frequently stored due to incorrect or insufficient diesel exhaust fluid
Disconnect associated controllers before probing circuits with the DVOM

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 specific repair steps may vary by make/model.

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 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 volts indicates a rich mixture. If the converter is working correctly, the downstream sensor should read 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 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 1” part of the code indicates the problem is with the engine’s first bank. That is, the bank that includes cylinder number 1. “Sensor 2” refers to the sensor mounted downstream of the catalytic converter.

Trouble code P042A is set when the PCM detects a malfunction in the Bank 1 Sensor 2 catalyst temperature sensor circuit.

Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P042A engine code may include:

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

Causes

Possible causes of this P042A 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 needed, 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 testing for this code varies 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 trouble 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 the scan tool on and choose the Bank 1 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’s 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 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 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 (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’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 (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’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 probe 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.

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 control 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 sensor (O2), 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 volts indicates a lean air/fuel mixture, while 0.9 volts indicates a rich mixture. If the converter is working properly, the downstream sensor should read steadily around 0.45 volts.

The efficiency and temperature of the catalytic converter go hand in hand. If the converter is working 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 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 1” part of the code indicates the issue is with the engine’s first bank. That is, the bank that includes cylinder number 1. “Sensor 2” refers to the sensor mounted downstream of the catalytic converter.

Trouble code P042B is set when the PCM detects a problem with the range or performance in the Bank 1 Sensor 2 catalyst temperature sensor circuit.

Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P042B engine code may include:

1. Check Engine Light illuminated
2. Poor engine performance
3. Reduced fuel economy
4. Increased emissions

Possible Causes of this P042B Code Include:

1. Faulty oxygen sensor
2. Wiring issues
3. Unbalanced air/fuel mixture
4. 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 necessary, 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 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 your 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 trouble codes are stored, you should address them 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 1 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 does not respond 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 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 which 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.

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 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 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 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 volts indicates a rich mixture. If the converter is working correctly, the downstream sensor should read 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 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 1” part of the code indicates the issue is with the engine’s first bank. That is, the bank that includes cylinder number 1. “Sensor 2” refers to the sensor mounted downstream of the catalytic converter.

Trouble code P042C is set when the PCM detects a low catalyst temperature sensor signal in bank 1, catalyst temperature sensor 2 circuit. This typically indicates the circuit is shorted.

Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P042C engine code may include:

• Check engine light illuminated
• Poor engine performance
• Reduced fuel economy
• Increased emissions

Causes

Possible causes of this P042C 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 your 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 trouble 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 1 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 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 (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’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 (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’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-probe 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.

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 specific repair steps may vary by make/model.

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 sensor (O2), 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 efficiency and temperature of the catalytic converter go hand in hand. If the converter is working 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 of a difference.

There is no actual “catalytic converter temperature sensor.” What the codes described in this article refer to is the oxygen sensor. The “bank 1” part of the code indicates the issue is with the engine’s first bank. That is, the bank that includes cylinder number 1. “Sensor 2” refers to the sensor mounted downstream of the catalytic converter.

Trouble code P042D is set when the PCM detects a high catalytic converter temperature sensor signal in bank 1, catalytic converter temperature sensor 2 circuit. This typically indicates an open circuit.
Code Severity and Symptoms

The severity of this code is moderate. Symptoms of a P042D engine code may include:

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

Causes

Possible causes of this P042D 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 necessary, 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 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

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 them first before proceeding with oxygen sensor diagnosis.
Check Sensor Operation

To do this, it is 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 1 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 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 the one on the scan tool. If the two do not match, the PCM is likely faulty or requires reprogramming.

What does it mean?

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

Basically, it means the downstream oxygen sensor for catalytic converter bank 2 detects the converter isn’t operating as efficiently as it should (to specifications). It’s part of the vehicle’s emission system.

Symptoms

You likely won’t notice any driveability problems, though there may be symptoms such as rough/harsh cold idle.

Causes

A P0430 code can mean one or more of the following has occurred:

• The catalytic converter is no longer working properly
• An oxygen sensor isn’t reading (functioning) correctly
• There’s an exhaust leak

Possible Solutions

First inspect for exhaust leaks.

The next step is to measure the voltage at the bank 2 oxygen sensor. Actually, it would be a good idea to test each O2 oxygen sensor while you’re at it.

One thing to note is that many automobile manufacturers offer longer warranties on emission-related parts. So if you have a newer car but it’s out of its bumper-to-bumper warranty, there may still be a warranty covering this type of issue. Many manufacturers offer a five-year unlimited mileage warranty on these items. It’s worth checking.

What does it mean?

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

Basically, it means the downstream oxygen sensor of the catalytic converter on bank 2 detects that the converter isn’t working as efficiently as it should (according to specifications). It’s part of the vehicle’s emission system.

Symptoms

You probably won’t notice any driving issues, although there might be symptoms such as rough/hard cold idle.

Causes

A P0431 code can mean one or more of the following has occurred:

The catalytic converter is no longer working properly
An oxygen sensor isn’t reading (functioning) correctly
There’s an exhaust leak

Possible Solutions

Inspect for exhaust leaks. The next step is to measure the voltage at the bank 2 oxygen sensor. Actually, it would be a good idea to test each O2 oxygen sensor while you’re at it.

One thing to note is that many automobile manufacturers offer longer warranties on emission-related parts. So if you have a newer car but it’s out of its bumper-to-bumper warranty, there might still be a warranty covering this type of issue. Many manufacturers offer a five-year unlimited mileage warranty on these items. It’s worth checking.