How Severe Is This DTC?
A stored P204C code should be considered severe and addressed as quickly as possible. The SCR system could be disabled because of this. Catalyst damage may occur if the conditions that contributed to storing the code are not corrected in a timely manner.
What Are Some of the Symptoms of the Code?
Symptoms of a P204C fault code may include:
- Reduced fuel efficiency
- Excessive black smoke from the vehicle’s exhaust
- Decreased engine performance
- Other SCR-related codes
What Are Some Common Causes of the Code?
Causes of this code may include:
- Faulty reductant pressure sensor
- Open or shorted circuits in the reductant pressure sensor system
- Faulty SCR controller/PCM or programming error
What Are the P204C Troubleshooting Steps?
A diagnostic scanner, digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information will be needed to diagnose a P204C code.
You can use your vehicle information source to locate a Technical Service Bulletin (TSB) that matches the vehicle’s year, make, and model; as well as engine size, stored codes, and presented symptoms. If you find one, it may provide useful diagnostic information.
Use the scanner (connected to the vehicle’s diagnostic connector) to retrieve all stored codes and relevant freeze frame data. It’s a good idea to record this information before clearing the codes, then test the vehicle until the PCM enters readiness mode or the code resets.
If the PCM enters readiness mode at this point, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions that contributed to storing the code may need to worsen before an accurate diagnosis can be made.
If the code immediately resets, the next step in your diagnosis will require you to search your vehicle information source for diagnostic flowcharts, connector pinout diagrams, connector face views, and component testing procedures/specifications.
Step 1
Use the DVOM to test the reductant pressure sensor according to manufacturer specifications. Components that test outside the allowable parameters should be considered faulty.
Step 2
If the actual reductant system pressure meets specifications, the P204C code persists, and the sensor in question is operational, use the DVOM to test the input and output signal circuits between the pressure sensor and the PCM/SCR controller. Disconnect all controllers before using the DVOM for testing.
Reductant pressure sensor codes are typically attributed to a leaking reductant system pump internally but complete your diagnosis