How Severe Is This DTC?
A stored P204D code should be considered severe and addressed as quickly as possible. The SCR system could be disabled because of this. Catalyst damage might 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 P204D trouble 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 P204D Troubleshooting Steps?
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a vehicle-specific diagnostic information source will be needed to diagnose a P204D 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 might 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 note 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 that point, the code is intermittent and may be much harder to diagnose. If that’s the case, the conditions that contributed to storing the code may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, 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 the manufacturer’s specifications. Components that do not test within the allowed maximum parameters should be considered faulty.
Step 2
If the actual reductant system pressure is within specifications, the P204D 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 often attributed to a leaking reductant system pump internally, but complete your diagnosis.