Technical Description of OBD-II Trouble Code
Leakage of Reductant
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Ford, Mercedes-Benz, Dodge, Chevrolet, and others. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P202D indicates that the powertrain control module (PCM) has detected insufficient activity in the control circuit for the reductant/regeneration supply pump.
The catalyst system is responsible for reducing almost all exhaust emissions, although certain applications also have a NOx trap.
Exhaust gas recirculation (EGR) systems go a step further in reducing NOx. However, larger and more powerful diesel engines today cannot meet strict federal (U.S.) emission standards with just the EGR, diesel particulate filter/catalytic converter, and NOx trap. This is why selective catalytic reduction (SCR) systems were invented.
SCR systems inject a reductant compound or diesel exhaust fluid (DEF) into the exhaust in front of the diesel particulate filter, NOx trap, and/or the catalytic converter using the reductant injection valve (solenoid). The precisely timed DEF injection raises the temperature of the filtration element, allowing it to perform more efficiently. This enhances the longevity of the filtration element and reduces harmful exhaust emissions released into the atmosphere. The entire SCR system is monitored and controlled by either the PCM or a stand-alone controller that interacts with the PCM. The controller monitors the O2, NOx, and exhaust temperature sensors, among 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.
The reductant/regeneration supply pump is used to pressurize the DEF in the liquid reductant system when required. The PCM monitors the supply pump voltage for consistent fluctuation and load percentage. The PCM also monitors one or more pressure sensors in the reductant supply system to detect any leaks.
If the PCM detects a degree of voltage variation on the reductant/regeneration supply circuit that is not within allowable parameters, a code P202F will be stored and a malfunction indicator lamp (MIL) may illuminate. Multiple ignition cycles with a failure may be required for MIL illumination.
What is the severity of this DTC?
A stored code P202D should be considered severe and addressed as quickly as possible. It could disable the SCR system, and catalyst damage could occur if the conditions contributing to the stored code are not rectified promptly.
What are some of the symptoms of the code?
Symptoms of a P202D trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P202D troubleshooting steps?
Ensure that the reductant/regeneration supply system is not losing pressure, both internally and externally. Activate the pump to create pressure and inspect the system for external leaks. Use a fuel pressure tester to manually monitor reductant system pressure. Check the supply pump and injector for any leaks. If any leaks are found, whether internal or external, they must be repaired before proceeding with the diagnosis.
To diagnose a code P202D, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle-specific diagnostic information.
You can consult your vehicle information source to find a technical service bulletin (TSB) that matches the vehicle’s year, make, and model, as well as the engine size, stored code/s, and exhibited symptoms. If you find a relevant TSB, it may provide helpful diagnostic information.
Use the scanner connected to the vehicle diagnostic connector to retrieve all stored codes and relevant freeze frame data. It is advisable to write down this information before clearing the codes and 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 point, the code is intermittent and may be more challenging to diagnose. In such cases, the conditions contributing to the stored 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 involve searching 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 system pressure sensors according to the manufacturer’s specifications. Any components that do not test within the maximum allowable parameters should be considered defective.
Step 2
Use your vehicle diagnostic information source and the DVOM to test the reductant supply pump voltage (usually battery voltage) with the pump activated. If current conditions do not allow activation, use the scanner to manually activate the pump.
Step 3
If the reductant supply pump is functioning properly, use the DVOM to test the input and output signal circuits from the fuse panel, PCM, and ignition switch. Disconnect all controllers before using the DVOM for testing.
