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OBD Codes
Your OBD-II Trouble Codes Repair Site

P204E Reductant Pressure Sensor Circuit Intermittent/Erratic

OBD-II Trouble Code Technical Description

Article by
Stephen Darby
Stephen Darby
ASE Certified Technician

总裁俱乐部appReductant Pressure Sensor Circuit Intermittent/Erratic

What does that mean?

总裁俱乐部appThis diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Dodge, Ram, VW, Audi, GMC, BMW, Mercedes-Benz, Ford, Chevrolet, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.


 

总裁俱乐部appA stored code P204E means that the powertrain control module (PCM) has detected an erratic degree of voltage in the reductant pressure sensor circuit. This code is exhibited in vehicles with a clean burning diesel engine, exclusively.

总裁俱乐部appThe catalyst system is responsible for reduction of (basically) all exhaust emissions although certain applications are also equipped with a NOx trap.

总裁俱乐部appExhaust gas recirculation (EGR) systems go another step further in the reduction of NOx. Nevertheless, today's larger and more powerful diesel engines cannot meet strict federal (U.S.) emission standards with the EGR, diesel particulate filter/catalytic converter, and NOx trap alone. It was for this reason that selective catalytic reduction (SCR) systems were invented.

总裁俱乐部appSCR systems inject a reductant compound or a diesel exhaust fluid (DEF) into the exhaust in front of the diesel particulate filter, NOx trap, and/or the catalytic converter via the reductant injection valve (solenoid). The precisely timed DEF injection elevates the temperature of the filtration element and allows it to perform more efficiently. It enhances filtration element longevity and allows fewer harmful exhaust emissions to be released into the atmosphere. The entire SCR system is monitored and controlled by either the PCM or a stand-alone controller (which interacts with the PCM). Either way, the controller monitors the O2, NOx, and exhaust temperature sensors (as well as other inputs) to determine the appropriate time for DEF (reductant) injection. Precise DEF injection is necessary to maintain exhaust temperature within acceptable parameters and optimize pollutant filtration.

总裁俱乐部appThe reductant/regeneration supply pump is used to pressurize the DEF in the liquid reductant system for use, when required. Supply pump voltage is monitored by the PCM for consistent fluctuation and load percentage. The PCM also monitors one or more pressure sensors in the reductant supply system to determine if there is a leak in the system.

总裁俱乐部appIf the PCM detects a degree of voltage in the reductant temperature sensor circuit that is erratic or intermittent and not within acceptable parameters, a code P204E will be stored and a malfunction indicator lamp (MIL) may be illuminated. Multiple ignition cycles (with a failure) may be required for MIL illumination.

Example of a DEF reductant tank:
P204E Example of a DEF Reductant Tank

What is the severity of this DTC?

总裁俱乐部appA stored code P204E should be considered severe and addressed as quickly as possible. The SCR system could be disabled because of it. Catalyst damage could result if the conditions which contributed to the code being stored are not rectified in a timely fashion.

What are some of the symptoms of the code?

总裁俱乐部appSymptoms of a P204E trouble code may include:

What are some of the common causes of the code?

总裁俱乐部appCauses for this code may include:

What are some P204E troubleshooting steps?

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P204E.

You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model; as well as the engine size, code/s stored, and symptoms exhibited. If you find one, it could yield helpful diagnostic information.

Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and pertinent freeze frame data. It is a good idea to write this information down before clearing the codes then test-drive the vehicle until the PCM either enters readiness mode or the code is reset.

If the PCM enters readiness mode at this time, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions which contributed to the code being stored may need to worsen before an accurate diagnosis can be made.

总裁俱乐部appIf the code is immediately reset, the next step of your diagnosis will require that you search your vehicle information source for diagnostic flow-charts, 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 manufacturer specifications. Components which do not test within maximum allowable parameters should be considered defective.

Step 2

If actual reductant system pressure is within specifications, the code P204E persists, and the sensor in question is in working order, use the DVOM to test input and output signal circuits between the pressure sensor and the PCM/SCR controller. Disconnect all controllers prior to using the DVOM for testing.

Related DTC Discussions

Need more help with a P204E code?

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NOTE: This information is presented for information purposes only. It is not intended as repair advice and we are not responsible for any actions you take on any vehicle. All information on this site is copyright protected.

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