BMW DTC C121B – Right Rear Wheel Speed Sensor Supply Voltage Circuit Low
DTC C121B meaning on BMW
DTC C121B on a BMW indicates a fault in the Right Rear Wheel Speed Sensor Supply Voltage Circuit. This fault means that the voltage in the circuit that supplies power to the right rear wheel speed sensor is lower than the expected value.
BMW DTC C121B symptoms
Symptoms of DTC C121B on a BMW may include:
- ABS warning light illuminated on the dashboard
- Traction control system malfunction
- Stability control system not functioning properly
- Loss of traction control during driving
BMW DTC C121B causes
Common causes of DTC C121B on a BMW include:
- Faulty right rear wheel speed sensor
- Corroded or damaged wiring in the circuit
- Loose or poor connection at the sensor or control module
- Defective ABS control module
BMW DTC C121B seriousness
DTC C121B should be taken seriously as it can affect the proper functioning of the ABS, traction control, and stability control systems in the vehicle. Driving with this fault unresolved may compromise the safety and stability of the vehicle, especially during emergency braking or slippery road conditions.
How to diagnose DTC C121B on BMW
To diagnose DTC C121B on a BMW, you can follow these steps:
- Use a diagnostic scanner to retrieve the fault codes from the ABS system
- Inspect the right rear wheel speed sensor and its wiring for any visible damage or corrosion
- Check the voltage supply to the sensor using a multimeter
- Inspect the connections at the sensor and ABS control module for any loose or poor connections
- If necessary, perform a continuity test on the wiring to ensure there are no breaks or shorts
How to fix DTC C121B on BMW
To fix DTC C121B on a BMW, you can try the following:
- Replace the right rear wheel speed sensor if it is found to be faulty
- Repair or replace any damaged or corroded wiring in the circuit
- Ensure all connections at the sensor and control module are secure and free of corrosion
- If the ABS control module is defective, it may need to be replaced or reprogrammed
How to erase DTC C121B on BMW
To erase DTC C121B on a BMW, you can use a diagnostic scanner to clear the fault codes stored in the ABS system. After fixing the underlying issue causing the fault code, clearing the code will reset the system and turn off the warning light on the dashboard.
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
Some of the links on this page may be affiliate links, which means we may earn a small commission if you make a purchase. This helps us keep our DTC database up to date and provide valuable content for free. We only recommend products that we have tested and believe to be the best in their class.