Technical Description of OBD-II Trouble Code
Correlation Issue between Reductant Injection Air Pressure Sensor A/B
What is the meaning of this?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to various OBD-II vehicles (1996-newer). This includes vehicles from BMW, Mercedes-Benz, Dodge, Sprinter, 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 P209E indicates that the powertrain control module (PCM) has detected a correlation problem between the reductant injection air pressure sensors A and B circuits. This system utilizes multiple pressure sensors. To determine which circuit is “A” and/or “B,” refer to a model-specific service manual.
The catalyst system is responsible for reducing almost all exhaust emissions, although some 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 developed.
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 using the reductant injection valve (solenoid). The precisely timed DEF injection raises the temperature of the filtration element, allowing it to function more efficiently. This improves 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 O2, NOx, and exhaust temperature sensors, among other inputs, to determine the appropriate time for DEF (reductant) injection. Precise DEF injection is crucial for maintaining exhaust temperature within acceptable parameters 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 a voltage correlation problem in the reductant injection air pressure sensors A and B circuits, it will store a code P209E and may illuminate the malfunction indicator lamp (MIL). Multiple ignition cycles with a failure may be required for MIL illumination.
How severe is this DTC?
A stored code P209E should be considered severe and addressed promptly. It could disable the SCR system, and catalyst damage may occur if the underlying conditions are not rectified in a timely manner.
What are some symptoms of the code?
Symptoms of a P209E trouble code may include:
What are some common causes of the code?
Possible causes for this code may include:
What are some troubleshooting steps for P209E?
Ensure that the reductant/regeneration supply system is not losing pressure internally or 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 leakage. If leaks are found, they must be repaired before proceeding with the diagnosis.
To diagnose a code P209E, 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’s year, make, and model, as well as the engine size, stored code/s, and exhibited symptoms. If a relevant TSB is found, 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 recommended 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 the 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 injection 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
If the reductant injection pressure is within specifications, the code P209E persists, and the sensor in question is functioning properly, 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.
