BMW DTC P21B4 – NOx Adsorber – Over Temperature, Bank 1
DTC P21B4 meaning on BMW
The DTC P21B4 code for BMW indicates a fault related to the NOx (nitrogen oxide) adsorber system on Bank 1 of the vehicle. This code specifically points to an over-temperature condition within the NOx adsorber system, which is designed to reduce harmful emissions by storing and then releasing nitrogen oxides.
BMW DTC P21B4 symptoms
Symptoms of the DTC P21B4 code on a BMW may include the illumination of the check engine light on the dashboard. In some cases, the vehicle may also experience reduced engine performance or efficiency due to the over-temperature condition in the NOx adsorber system.
BMW DTC P21B4 causes
The DTC P21B4 code on a BMW can be triggered by various factors, including a malfunctioning NOx sensor, a faulty NOx adsorber, issues with the exhaust gas recirculation (EGR) system, or problems with the engine control module (ECM) that manages the NOx adsorber system.
BMW DTC P21B4 seriousness
The DTC P21B4 code should not be ignored, as it indicates a potential problem with the vehicle’s emissions control system. Driving with this fault unresolved may lead to increased emissions and could potentially cause the vehicle to fail emissions tests.
How to diagnose DTC P21B4 on BMW
To diagnose the DTC P21B4 code on a BMW, a mechanic would typically use a diagnostic scanner to retrieve the fault codes stored in the vehicle’s ECM. They would then perform a visual inspection of the NOx adsorber system components, check the NOx sensor readings, and test the EGR system for proper operation.
How to fix DTC P21B4 on BMW
Fixing the DTC P21B4 code on a BMW may involve replacing the NOx sensor, repairing or replacing the NOx adsorber, addressing any issues with the EGR system, or reprogramming the ECM to correct the over-temperature condition. It is recommended to consult with a qualified mechanic or dealership for proper diagnosis and repair.
How to erase DTC P21B4 on BMW
Once the underlying issue causing the DTC P21B4 code on a BMW has been resolved, the fault codes can be cleared using a diagnostic scanner. This will reset the check engine light and erase the DTC P21B4 code from the vehicle’s ECM memory.
Recommended tools & DTC Scanners for BMW
Best Diagnostic App for modern BMWs: BimmerLink
Recommended Bluetooth adapter for Bimmerlink: OBDLink CX
Cable adapter for Bimmerlink: Enet Cable USB Type C
For older BMWs we recommend: Autel AutoLink AL319 (2024 version)
Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter
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