Technical Description of OBD-II Trouble Code
EGR Deactivation – NOx Exceedance
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all diesel vehicles (Ford, Dodge, Chevrolet, GMC, Ram, VW, etc.) manufactured from 1996 onwards. While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The P2BAC code is unique in that it is an information-only code. It is not intended for diagnosis, but rather to alert you that another problem exists and the exhaust gas recirculation (EGR) system has been deactivated. A P2BAC code should always be accompanied by other exhaust or EGR related codes. The other codes must be diagnosed and repaired before addressing this code, as fixing the underlying conditions that caused the other codes to be stored will almost always rectify the P2BAC code. It is important to note that this type of code is typically found in diesel-powered vehicles only.
When this code is stored, it indicates that the PCM has detected a level of nitrogen oxide (NOx) that exceeds a programmed limit. This detection may have occurred in the NOx trap or the diesel particulate filter (DPF). It could also be due to a faulty DPF pressure sensor or NOx sensor.
As an additional note: Some diesel-powered Dodge and Ram trucks manufactured between 2007 and 2012 are equipped with catalytic converters and oxygen (O2) sensors. These vehicles are particularly susceptible to these types of codes. In these cases, the P2BAC code is usually accompanied by an O2 sensor code. By diagnosing and repairing the O2 sensor code, the P2BAC code will typically disappear.
Most modern diesel-powered vehicles are equipped with DPF systems that reduce soot particles and black smoke emissions. The DPF is a component of the exhaust system and is equipped with pressure sensors that are monitored by the powertrain control module (PCM). When the DPF pressure exceeds a programmed level, the filtration element should be rejuvenated. Rejuvenation methods for the filtration element include active and passive methods. Active filtration occurs automatically while the vehicle is in operation. Passive rejuvenation typically occurs after the vehicle has been parked and requires manual activation. To determine the type of system equipped in your vehicle, consult a reliable source of vehicle information.
If the rejuvenation process is not fully completed, or if it does not occur at regular intervals, DPF pressure codes will be stored, which may also be accompanied by a P2BAC code.
Other diesel-powered vehicles use NOx trap systems as an additional measure to reduce emissions. Some vehicles even utilize both a DPF and a NOx trap for enhanced emission control. The NOx trap is another component in the exhaust system that captures NOx particles and must be rejuvenated regularly. Similar to the DPF system, if the NOx trap is not rejuvenated regularly, exhaust pressure will increase and a NOx trap code will be stored. In these cases, a P2BAC code may also accompany the NOx system codes.
The EGR system is designed to supply a portion of spent exhaust gases to the engine induction system. In the engine, excessive fuel is burned from the exhaust, reducing the amount of NOx produced by exhaust emissions. When the PCM detects exhaust pressure indicative of an unacceptably high level of NOx (in the DPF, NOx trap, or catalytic converter), the EGR system will be deactivated to reduce stress on the affected component and decrease exhaust pressure. In this scenario, the P2BAC code will be stored. The malfunction indicator lamp (MIL) will not illuminate solely because the P2BAC code is stored. MIL illumination will occur due to the accompanying DPF, NOx, and O2 sensor codes that are stored.
Severity & Symptoms
The severity of a stored P2BAC code depends on the accompanying codes present. The P2BAC code itself does not have any symptoms directly associated with it.
Symptoms of accompanying codes may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
To diagnose the codes that accompany a P2BAC, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), an infrared thermometer, and a reliable source of vehicle information (such as All Data).
I would start by ensuring that the vehicle has an adequate amount of the correct type of DPF or NOx trap regeneration fluid. Since the P2BAC code is a direct result of a stored DPF, NOx trap, or O2 sensor code, I would first diagnose and repair any other codes that are present. Addressing the DPF and/or NOx trap regeneration fluid may resolve the conditions causing these types of codes to be stored.
Certain driving habits can also affect DPF and NOx trap regeneration. Short trips and trips that do not require the engine to be under sufficient load may not allow for adequate DPF and/or NOx trap regeneration. By using the appropriate diagnostic information for the codes that accompany a P2BAC, diagnosing and repairing them first, the P2BAC code should disappear.
Additional diagnostic notes:
