BMW DTC P21C2 – Reductant Heater Relay Control Circuit/Open
DTC P21C2 meaning on BMW
The DTC P21C2 code on a BMW indicates a fault in the reductant heater relay control circuit, specifically an open circuit. The reductant heater relay is responsible for controlling the heating element in the diesel exhaust fluid (DEF) tank to prevent freezing in cold temperatures and ensure proper operation of the selective catalytic reduction (SCR) system.
BMW DTC P21C2 symptoms
Symptoms of the DTC P21C2 code on a BMW may include:
- Check Engine Light (CEL) illuminated
- Reduced engine performance
- Possible DEF system warning message
BMW DTC P21C2 causes
Common causes of the DTC P21C2 code on a BMW include:
- Faulty reductant heater relay
- Open or short circuit in the relay control circuit
- Defective wiring or connectors
BMW DTC P21C2 seriousness
The DTC P21C2 code should not be ignored as it can lead to reduced engine performance and potential emissions issues. It is recommended to address this issue promptly to ensure proper operation of the DEF system and maintain vehicle performance.
How to diagnose DTC P21C2 on BMW
To diagnose the DTC P21C2 code on a BMW, you can follow these steps:
- Use a diagnostic scanner to retrieve the fault codes stored in the vehicle’s computer.
- Inspect the reductant heater relay and its wiring for any visible damage or corrosion.
- Check the relay control circuit for continuity and proper voltage levels.
- Perform a resistance test on the reductant heater relay to determine if it is functioning correctly.
How to fix DTC P21C2 on BMW
To fix the DTC P21C2 code on a BMW, you can try the following solutions:
- Replace the faulty reductant heater relay with a new one.
- Repair any open or short circuits in the relay control circuit.
- Inspect and repair any damaged wiring or connectors in the system.
- Clear the fault codes using a diagnostic scanner after completing the repairs.
How to erase DTC P21C2 on BMW
To erase the DTC P21C2 code on a BMW, you can use a diagnostic scanner to clear the fault codes stored in the vehicle’s computer. After addressing the underlying issue causing the fault code and making the necessary repairs, you can reset the system by clearing the codes to turn off 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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