What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles (Dodge, Ram, Ford, GMC, Chevrolet, VW, Audi, Toyota, etc.). Although generic, specific repair steps may vary by make/model.
When I diagnosed a P0424 code, I found that the Powertrain Control Module (PCM) detected a problem with the heated catalytic converter temperature for engine bank one. Bank 1 indicates the problem occurred in the engine bank containing cylinder number one.
While I cannot state with absolute certainty that a P0424 code only applies to diesel engine vehicles; I have never seen it exposed in anything other than diesel engine vehicles.
Heated catalytic converters are used to reduce exhaust emissions produced by diesel engines. A filtration block, composed of ceramic fibers interwoven with platinum and other precious metals, enclosed in an inline steel housing and placed in the exhaust system, is the key component of the heated catalytic converter. Beyond the heat created as a byproduct of engine exhaust, diesel engine exhaust frequently needs to be heated further to sufficiently reduce nitrogen oxide particles (N2O), carbon monoxide, and unburned hydrocarbons into harmless ions of nitrogen, oxygen, carbon dioxide, and water. Temperatures inside the heated catalytic converter are often designed to reach a minimum of 1,200 degrees Fahrenheit. To produce the extreme temperatures needed to reduce emissions from diesel engines, diesel exhaust fluid is injected into the heated catalyst at intervals controlled by the PCM.
Upstream and downstream exhaust temperature sensors are used by the PCM to monitor the heated catalytic converter threshold. This is necessary to ensure the filtration element (catalyst) is sufficiently heated.
Exhaust gases are pushed through the manifold, into the exhaust pipe, past the upstream exhaust temperature sensor, and through the heated catalytic converter. After passing through the heated catalytic converter, they pass the downstream exhaust temperature sensor. The PCM is programmed with specific minimum requirements regarding the temperature differential between exhaust gases entering the catalyst and exhaust gases exiting the catalyst. These programmed requirements are referred to here as the heated catalyst temperature threshold.
If the heated catalyst temperature variation (between the upstream and downstream exhaust temperature sensors) is below the minimum allowed threshold, a P0424 code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated.
Other Bank 1 catalyst malfunction codes include P0420, P0421, P0422, P0423, P0425, P0426, P0427, P0428, and P0429.
Code Severity and Symptoms
If a P0424 code has been stored in your vehicle, it may indicate that the diesel exhaust fluid injection system is not functioning. This code should be classified as severe.
Symptoms of this code may include:
- Decreased fuel efficiency
- Lack of overall engine performance
- Excessive black smoke from the exhaust
- Other related diagnostic codes
- MIL (Malfunction Indicator Lamp) illumination
Causes
Possible causes for this code being set are as follows:
- Faulty diesel exhaust fluid injection system
- Inadequate diesel exhaust fluid
- Faulty exhaust temperature sensor(s)
- Burned, broken, or disconnected wiring and/or connectors
Diagnostic and Repair Procedures
To diagnose a P0424 code, I would need a diagnostic scanner, a digital volt/ohmmeter (DVOM), an infrared thermometer (preferably with a laser pointer), and a reliable vehicle information source (such as All Data DIY).
Before attempting to diagnose a stored P0424 code, all codes related to the diesel exhaust fluid injection system should be addressed, and the engine must be running efficiently.
I normally start with a visual inspection of the system’s wiring harnesses and connectors, focusing on harnesses routed near hot exhaust pipes and manifolds, as well as those near sharp objects like 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’ve found that writing down this information can prove helpful later in my diagnosis. Now, I would clear the codes and test drive the vehicle to see if the P0424 immediately resets.
I would start the engine and allow it to reach normal operating temperature if the P0424 is reset. I would test drive the vehicle while carefully using the scanner’s data stream to observe the exhaust temperature sensor input data. Limiting the data stream to include only relevant data will provide a more accurate data sample.
Once the PCM enters closed-loop operation and driving conditions are met for the diesel exhaust fluid injection system to be activated, the exhaust gas temperature sensor signals should reach an acceptable threshold and remain relatively stable. If not, access the catalytic converter by placing the vehicle on a lift or hoist and use the infrared thermometer to take a manual temperature reading of the exhaust pipe in the immediate vicinity of the exhaust temperature sensor(s). Compare the temperature displayed on the infrared thermometer with the data presented on the scanner to determine if there is a problem with either exhaust temperature sensor.
Consult your vehicle information source for the vehicle’s recommended specifications and use the DVOM to check the resistance of the exhaust temperature sensor in question.
Additional diagnostic notes:
- The presence of a stored P0424 does not often condemn the catalytic converter
- Exhaust temperature sensor failure is more common than catalytic converter failure
- Diesel exhaust fluid must be present and of the correct type before diagnosing a P0424
- Disconnect all associated controllers before attempting to test system circuit resistance with the DVOM