BMW DTC P21C8 – Reductant Control Module Power Relay/Relays Control Circuit Low
DTC P21C8 meaning on BMW
DTC P21C8 on a BMW refers to an issue with the Reductant Control Module Power Relay/Relays Control Circuit being detected as low. The reductant control module is responsible for managing the urea injection system in vehicles equipped with Selective Catalytic Reduction (SCR) technology. This fault code indicates a problem with the power relay or relays that control the reductant module’s operation.
BMW DTC P21C8 symptoms
Symptoms of DTC P21C8 on a BMW may include the Check Engine Light being illuminated on the dashboard. In some cases, the vehicle may go into a reduced power mode or fail to start. Additionally, there may be a decrease in fuel efficiency or performance.
BMW DTC P21C8 causes
The causes of DTC P21C8 on a BMW can vary, but common reasons include a faulty power relay, damaged wiring or connectors in the control circuit, or a malfunctioning reductant control module. Corrosion or poor connections can also lead to this fault code.
BMW DTC P21C8 seriousness
DTC P21C8 should be addressed promptly to prevent potential damage to the vehicle’s emissions system. Ignoring this fault code can lead to increased emissions, reduced fuel efficiency, and possible engine performance issues. While the vehicle may still be operable with this fault, it is recommended to have it diagnosed and repaired as soon as possible.
How to diagnose DTC P21C8 on BMW
To diagnose DTC P21C8 on a BMW, a mechanic would typically use a diagnostic scanner to retrieve the fault code and perform a thorough inspection of the reductant control module, power relay, wiring, and connectors. They may also conduct tests to check the functionality of the components involved in the control circuit.
How to fix DTC P21C8 on BMW
Fixing DTC P21C8 on a BMW may involve replacing the faulty power relay, repairing damaged wiring or connectors, or replacing the reductant control module if necessary. It is essential to follow the manufacturer’s diagnostic and repair procedures to ensure the issue is resolved correctly.
How to erase DTC P21C8 on BMW
Once the underlying issue causing DTC P21C8 on a BMW has been fixed, the fault code can be cleared using a diagnostic scanner. By erasing the code, the Check Engine Light should turn off. It is important to verify that the repair was successful by driving the vehicle and rescanning for any remaining fault codes.
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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