P209B Reductant Injection Air Pressure Sensor Circuit Range / Performance B

P209B Reductant Injection Air Pressure Sensor Circuit Range / Performance B

OBD-II DTC Datasheet

Reductant B Injection Air Pressure Sensor Circuit Out of Range / Performance

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code and applies to many OBD-II vehicles (1996 and newer). This may include, but is not limited to, BMW, Mercedes-Benz, Dodge, Sprinter, etc. Despite the general nature, the exact repair steps may vary depending on the model year, make, model and transmission configuration.

A stored code P209B means the powertrain control module (PCM) has detected a voltage level on the reductant injection air pressure sensor B circuit that is outside the normal range. The B designation indicates a specific sensor in a system that can use multiple pressure sensors. Refer to the service manual for your particular model to determine which circuit is "B".

The catalyst system is responsible for reducing (mostly) all exhaust emissions, although some applications are also equipped with a NOx trap.

Exhaust Gas Recirculation (EGR) systems take another step in reducing NOx emissions. However, today's larger, more powerful diesel engines cannot meet strict federal (US) emission standards with just an EGR system, a particulate filter / catalytic converter, and a NOx trap. For this reason, selective catalytic reduction (SCR) systems have been invented.

SCR systems inject a reductant formulation or Diesel Exhaust Fluid (DEF) into the exhaust gases upstream of the particulate filter, NOx trap and / or catalytic converter through a reductant injection valve (solenoid). The precisely calculated DEF injection raises the temperature of the filter element and allows it to work more efficiently. It extends the service life of the filter elements and helps reduce emissions of harmful exhaust gases into the atmosphere. The entire SCR system is controlled and monitored by either the PCM or a stand-alone controller (which interacts with the PCM). In any case, the controller monitors the O2, NOx and exhaust gas temperature sensors (as well as other inputs) to determine the appropriate timing for the DEF (reductant) injection. Precision DEF injection is required to keep the exhaust gas temperature within acceptable parameters and to optimize the filtration of pollutants.

The reductant / regeneration pump is used to pressurize the DEF in the reductant liquid system for use when needed. The PCM monitors the supply pump voltage for continuous fluctuations 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 on the reductant injection air pressure sensor B circuit that is outside the normal range, a code P209B will be stored and a malfunction indicator lamp (MIL) may come on. MIL illumination may require multiple ignition cycles - in case of failure.

What is the severity of this DTC?

A stored P209B code should be treated as serious and should be dealt with as soon as possible. The SCR system could be disabled because of this. Catalyst damage can occur if the conditions that contributed to the persistence of the code are not corrected in a timely manner.

What are some of the symptoms of the code?

Symptoms of a P209B trouble code may include:

• Decreased fuel efficiency
• Excessive black smoke from vehicle exhaust
• Reduced engine performance
• Other codes related to SCR

What are some of the common causes for the code?

Reasons for this code may include:

• Reducing agent air pressure sensor defective (B)
• Open or short circuit in a chain in the system of the air pressure sensor for injection of a reductant
• Bad SCR / PCM controller or programming error

What are some steps to troubleshoot the P209B?

Make sure the reductant / regeneration system does not lose pressure (internal or external). Turn on the pump to build up pressure and check the system for external leaks. Use a fuel pressure tester to manually monitor the pressure in the reductant system. Check the feed pump and nozzle for leaks. If leaks (internal or external) are found, they must be repaired before continuing with the diagnosis.

To diagnose the P209B code, you will need a diagnostic scanner, a digital volt / ohmmeter (DVOM), and a source of vehicle-specific diagnostic information.

You can use your vehicle information source to find a Technical Service Bulletin (TSB) that matches your vehicle's year, make and model; as well as engine displacement, stored codes and symptoms detected. If you find it, it can provide useful diagnostic information.

Use a scanner (connected to the vehicle's diagnostic socket) to retrieve all stored codes and associated freeze frame data. It is recommended that you write down this information before clearing the codes and then test drive the vehicle until the PCM enters ready mode or the code is cleared.

If the PCM enters ready mode at this time, the code is intermittent and can be much more difficult to diagnose. In this case, the conditions that contributed to the retention of the code may need to worsen before an accurate diagnosis can be made.

If the code is reset immediately, the next diagnostic step will require you to search your vehicle information source for diagnostic block diagrams, pinouts, connector faceplates, and component test procedures / specifications.

Step 1

Use the DVOM to test the pressure sensors of the reductant injection system according to the manufacturer's specifications. Components that fail the test within the maximum allowable parameters should be considered defective.

Step 2

If the injection pressure of the reductant is within specifications, the P209B code persists and the sensor in question is operational, use the DVOM to test the input and output circuits between the sensors and the PCM / SCR controller. Disconnect all controllers before using the DVOM for testing.

• Reductant nozzle sensor codes are often associated with feed pumps that are leaking internally.

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