Technical Description of OBD-II Trouble Code
The circuit range/performance of the Reductant Injection Air Pressure Sensor A is being detected by this diagnostic trouble code (DTC). It is a generic powertrain code that applies to various OBD-II vehicles (1996-newer), including BMW, Mercedes-Benz, Dodge, Sprinter, and others. The repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P2038 indicates that the powertrain control module (PCM) has detected an abnormal voltage in the reductant injection air pressure sensor A circuit. To determine which circuit is the “A” circuit, refer to a model-specific service manual.
The catalyst system is responsible for reducing exhaust emissions, and some applications also have a NOx trap. Exhaust gas recirculation (EGR) systems further reduce NOx. However, larger and more powerful diesel engines cannot meet strict emission standards with just the EGR, diesel particulate filter/catalytic converter, and NOx trap. This led to the invention of selective catalytic reduction (SCR) systems.
SCR systems inject a reductant compound or diesel exhaust fluid (DEF) into the exhaust before the diesel particulate filter, NOx trap, and/or catalytic converter. The precise timing of DEF injection improves the efficiency of the filtration element, prolongs its lifespan, and reduces harmful exhaust emissions. The entire SCR system is monitored and controlled by the PCM or a stand-alone controller. The controller uses input from O2, NOx, and exhaust temperature sensors to determine the optimal time for DEF injection.
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 pressure sensors in the reductant supply system to detect any leaks.
If the PCM detects an abnormal voltage in the reductant injection air pressure sensor A circuit, it stores a code P2038 and may illuminate the malfunction indicator lamp (MIL). Multiple ignition cycles with a failure may be required for MIL illumination.
Severity of this DTC
A stored code P2038 should be considered severe and addressed promptly. It could disable the SCR system and potentially cause catalyst damage if the underlying conditions are not resolved in a timely manner.
Symptoms of the code
Symptoms of a P2038 trouble code may include:
Common causes of the code
Possible causes for this code include:
Troubleshooting steps for P2038
Ensure that the reductant/regeneration supply system does not have any internal or external pressure loss. Activate the pump to create pressure and inspect the system for leaks. Use a fuel pressure tester to manually monitor reductant system pressure. Check the supply pump and injector for leakage. Repair any leaks (internal or external) before proceeding with the diagnosis.
To diagnose a code P2038, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and vehicle-specific diagnostic information. Refer to your vehicle information source to find a technical service bulletin (TSB) that matches the vehicle details and symptoms. This may provide helpful diagnostic information.
Use the scanner to retrieve all stored codes and freeze frame data. Write down this information before clearing the codes and 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 conditions contributing to the code being stored may need to worsen for an accurate diagnosis.
If the code is immediately reset, you will need to consult 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 injection system pressure sensors according to manufacturer specifications. Consider components defective if they do not test within the maximum allowable parameters.
Step 2
If the reductant injection pressure is within specifications, the code P2038 persists, and the sensor is functioning correctly, use the DVOM to test the input and output signal circuits between the sensors and the PCM/SCR controller. Disconnect all controllers before conducting the DVOM tests.
