P209C Reductant Injection Air Pressure Sensor B Circuit Low

Description and meaning of DTC p209c

This 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 BMW, Mercedes-Benz, Dodge, Sprinter, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration. A stored code P209C means that the powertrain control module (PCM) has detected an insufficient degree of voltage in the reductant injection air pressure sensor B circuit. The denotation B indicates a particular sensor in a system which may use multiple pressure sensors. Refer to a model specific service manual to determine which is the B circuitThe catalyst system is responsible for reduction of (basically) all exhaust emissions although certain applications are also equipped with a NOx trap. Exhaust 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. SCR 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. The 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. If the PCM detects a degree of voltage in the reductant injection air pressure sensor B circuit that is insufficient, a code P209C will be stored and a malfunction indicator lamp (MIL) may be illuminated. Multiple ignition cycles - with a failure - may be required for MIL illumination.

p209c diagnostic trouble code symptoms

Symptoms of a P209C trouble code may include:Reduction in fuel efficiencyExcessive black smoke from vehicle exhaustDiminished engine performanceOther SCR related codes

DTC p209c - possible causes

Causes for this code may include:Defective reductant air pressure sensor (B)Open or shorted circuits in the reductant injection air pressure sensor systemBad SCR controller/PCM or programming error

How to fix OBD-II diagnostic trouble code p209c

Make sure 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 monitor reductant system pressure manually. Check the supply pump and the injector for leakage. If leaks are discovered (internal or external), they must be repaired before continuing with the diagnosis. A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P209C. 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. If 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.

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