BMW DTC P21AC – Reductant Level Sensor ‘B’ Circuit Intermittent/Erratic
DTC P21AC meaning on BMW
The DTC P21AC code on a BMW indicates an issue with the Reductant Level Sensor ‘B’ circuit being intermittent or erratic. This sensor is responsible for monitoring the level of the diesel exhaust fluid (DEF), also known as AdBlue, in the vehicle’s tank.
BMW DTC P21AC symptoms
Symptoms of the DTC P21AC code on a BMW may include:
- Check Engine Light (MIL) illuminated
- Reduced engine performance
- Possible DEF system warnings
BMW DTC P21AC causes
Common causes of the DTC P21AC code on a BMW include:
- Defective Reductant Level Sensor ‘B’
- Wiring or connector issues in the sensor circuit
- Corrosion or contamination in the sensor or tank
BMW DTC P21AC seriousness
While the DTC P21AC code may not cause immediate drivability issues, it is important to address it promptly to ensure proper operation of the DEF system. Ignoring this code can lead to emissions non-compliance and potential long-term engine damage.
How to diagnose DTC P21AC on BMW
To diagnose the DTC P21AC code on a BMW, a mechanic may perform the following steps:
- Use a diagnostic scanner to retrieve the fault codes and freeze frame data
- Inspect the Reductant Level Sensor ‘B’ and its wiring for any visible damage or corrosion
- Test the sensor’s resistance and voltage readings according to manufacturer specifications
- Check the DEF tank for contamination or blockages
How to fix DTC P21AC on BMW
To fix the DTC P21AC code on a BMW, the following steps may be taken:
- Replace the Reductant Level Sensor ‘B’ if it is found to be faulty
- Repair any damaged wiring or connectors in the sensor circuit
- Clean the sensor and DEF tank of any contamination or debris
- Clear the fault codes and perform a test drive to ensure the issue is resolved
How to erase DTC P21AC on BMW
To erase the DTC P21AC code on a BMW, a diagnostic scanner can be used to clear the fault codes stored in the vehicle’s ECU. After the repair has been completed and the underlying issue resolved, the code can be cleared to reset the Check Engine Light.
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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