Technical Description of OBD-II Trouble Code
The circuit for the Reductant Pressure Sensor is experiencing intermittent or erratic behavior.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to many OBD-II vehicles (1996-newer). This includes vehicles from various manufacturers such as Dodge, Ram, VW, Audi, GMC, BMW, Mercedes-Benz, Ford, Chevrolet, etc. While the code is generic, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
A stored code P204E indicates that the powertrain control module (PCM) has detected inconsistent voltage levels in the reductant pressure sensor circuit. This code is typically found in vehicles with clean burning diesel engines.
The catalyst system is responsible for reducing exhaust emissions, including NOx. Some applications also have a NOx trap.
Exhaust gas recirculation (EGR) systems further reduce NOx emissions. However, larger and more powerful diesel engines cannot meet strict U.S. emission standards with just the EGR, diesel particulate filter/catalytic converter, and NOx trap. This led to the development of selective catalytic reduction (SCR) systems.
SCR systems inject a reductant compound or diesel exhaust fluid (DEF) into the exhaust system before the diesel particulate filter, NOx trap, and/or catalytic converter. The precise injection of DEF raises the temperature of the filtration element, improving its efficiency. This extends the lifespan of the filtration element and reduces harmful exhaust emissions. The entire SCR system is monitored and controlled by the PCM or a stand-alone controller, which interacts with the PCM. The controller monitors sensors for O2, NOx, and exhaust temperature, among other inputs, to determine the optimal time for DEF injection. Accurate DEF injection is crucial for maintaining acceptable exhaust temperature and optimizing pollutant filtration.
The reductant/regeneration supply pump pressurizes the DEF in the liquid reductant system when needed. The PCM monitors the supply pump voltage for consistent fluctuation and load percentage. It also monitors one or more pressure sensors in the reductant supply system to detect any leaks.
If the PCM detects erratic or intermittent voltage in the reductant temperature sensor circuit that falls outside acceptable parameters, it will store a code P204E and may illuminate the malfunction indicator lamp (MIL). The MIL may require multiple ignition cycles with a failure for illumination.
Example of a DEF reductant tank:
What is the severity of this DTC?
A stored code P204E should be considered severe and addressed as quickly as possible. It could disable the SCR system and potentially cause catalyst damage if the underlying conditions are not resolved promptly.
What are some of the symptoms of the code?
Symptoms of a P204E trouble code may include:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P204E troubleshooting steps?
To diagnose a code P204E, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and access to vehicle-specific diagnostic information.
Refer to your vehicle information source to find a technical service bulletin (TSB) that matches the vehicle’s year, make, model, engine size, stored codes, and exhibited symptoms. A relevant TSB may provide helpful diagnostic information.
Use the scanner connected to the vehicle diagnostic connector to retrieve all stored codes and freeze frame data. It is recommended to write down this information before clearing the codes and then test-drive the vehicle until the PCM enters readiness mode or the code is reset.
If the PCM enters readiness mode, the code is intermittent and may be more challenging to diagnose. In such cases, the underlying conditions may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, the next step in the diagnosis involves consulting your vehicle information source for diagnostic flowcharts, connector pin-out charts, 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. Any components that do not meet the maximum allowable parameters should be considered defective.
Step 2
If the actual reductant system pressure is within specifications, the code P204E persists, and the sensor in question is functioning correctly, use the DVOM to test the input and output signal circuits between the pressure sensor and the PCM/SCR controller. Disconnect all controllers before conducting the DVOM tests.
