BMW DTC P21CD – Reductant Quality Module Supply Voltage Low
DTC P21CD meaning on BMW
The DTC P21CD on a BMW indicates a fault with the Reductant Quality Module Supply Voltage being low. The Reductant Quality Module is responsible for monitoring the quality of the diesel exhaust fluid (DEF) in the vehicle’s emissions system.
BMW DTC P21CD symptoms
Symptoms of the DTC P21CD on a BMW may include the check engine light illuminating on the dashboard, reduced engine performance, and potential issues with the vehicle’s emissions system.
BMW DTC P21CD causes
The low supply voltage to the Reductant Quality Module in a BMW can be caused by a faulty module, damaged wiring, a blown fuse, or issues with the vehicle’s electrical system.
BMW DTC P21CD seriousness
While the DTC P21CD may not cause immediate drivability issues, it is important to address this fault promptly to ensure proper functioning of the emissions system and to prevent potential long-term damage to the vehicle.
How to diagnose DTC P21CD on BMW
To diagnose the DTC P21CD on a BMW, a mechanic would typically use a diagnostic scanner to retrieve the fault code and then perform further testing to pinpoint the exact cause. This may involve checking the wiring, inspecting the Reductant Quality Module, and testing the vehicle’s electrical system.
How to fix DTC P21CD on BMW
Fixing the DTC P21CD on a BMW may involve repairing or replacing the Reductant Quality Module, repairing any damaged wiring, replacing blown fuses, or addressing any underlying electrical issues in the vehicle.
How to erase DTC P21CD on BMW
Once the underlying issue causing the DTC P21CD on a BMW has been fixed, the fault code can be erased using a diagnostic scanner. This will clear the code from the vehicle’s memory and 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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