P21AB – BMW DTC

BMW DTC P21AB – Reductant Level Sensor ‘B’ Circuit High

DTC P21AB meaning on BMW

The DTC P21AB error code on a BMW indicates an issue with the Reductant Level Sensor ‘B’ Circuit High. This sensor is responsible for monitoring the level of the diesel exhaust fluid (DEF), also known as AdBlue, in the vehicle’s emission control system. A high circuit reading suggests that the sensor is detecting a higher than normal fluid level, which could be due to a malfunction in the sensor or the wiring associated with it.

BMW DTC P21AB symptoms

Symptoms of the DTC P21AB error code on a BMW may include:

• Check Engine Light illuminated on the dashboard
• Reduced engine performance
• Increased fuel consumption
• Possible DEF system warnings

BMW DTC P21AB causes

The common causes of the DTC P21AB error code on a BMW are:

• Defective Reductant Level Sensor ‘B’
• Wiring issues such as shorts or open circuits
• Corrosion or poor connections in the sensor circuit

BMW DTC P21AB seriousness

While the DTC P21AB error code may not cause immediate drivability issues, it is important to address it promptly to ensure proper functioning of the vehicle’s emission control system. Ignoring this code can lead to increased emissions and potential damage to the catalytic converter.

How to diagnose DTC P21AB on BMW

To diagnose the DTC P21AB error code on a BMW, you can follow these steps:

1. Use a diagnostic scanner to retrieve the fault codes stored in the vehicle’s computer.
2. Inspect the Reductant Level Sensor ‘B’ and its wiring for any visible damage or corrosion.
3. Perform a resistance test on the sensor to check for proper functionality.
4. Check the DEF fluid level to ensure it is within the correct range.

How to fix DTC P21AB on BMW

To fix the DTC P21AB error code on a BMW, you can try the following solutions:

1. Replace the Reductant Level Sensor ‘B’ if it is found to be faulty.
2. Repair any damaged wiring or connections in the sensor circuit.
3. Clean any corrosion from the sensor terminals and ensure a secure connection.
4. Reset the fault codes using a diagnostic scanner after completing the repairs.

How to erase DTC P21AB on BMW

To erase the DTC P21AB error code on a BMW, you can use a diagnostic scanner to clear the fault codes stored in the vehicle’s computer. After making the necessary repairs and ensuring that the issue has been resolved, you can reset the codes to turn off the Check Engine Light and monitor the system for any recurring issues.

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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