BMW DTC P121C – NOx Sensor Heater Control Circuit Shorted (Bank 1)
DTC P121C meaning on BMW
DTC P121C on a BMW indicates a fault with the NOx (Nitrogen Oxide) sensor heater control circuit in Bank 1. This fault code is specifically related to the heating element of the NOx sensor, which is responsible for ensuring accurate readings of NOx levels in the exhaust gases.
BMW DTC P121C symptoms
Symptoms of DTC P121C on a BMW may include:
- Check Engine Light (MIL) illuminated
- Reduced engine performance
- Increased fuel consumption
- Possible emissions issues
BMW DTC P121C causes
Common causes of DTC P121C on a BMW include:
- Short circuit in the NOx sensor heater control circuit
- Faulty NOx sensor heater
- Wiring or connector issues
- ECU (Engine Control Unit) malfunction
BMW DTC P121C seriousness
DTC P121C should not be ignored as it can lead to increased emissions, reduced engine efficiency, and potential damage to the catalytic converter. It is important to address this issue promptly to maintain the vehicle’s performance and comply with emissions regulations.
How to diagnose DTC P121C on BMW
To diagnose DTC P121C on a BMW, you can follow these steps:
- Use a diagnostic scanner to retrieve the fault code and freeze frame data
- Inspect the NOx sensor heater control circuit for any visible damage or corrosion
- Check the wiring and connectors for continuity and proper connection
- Test the NOx sensor heater for resistance and functionality
- Perform a thorough inspection of the ECU for any signs of malfunction
How to fix DTC P121C on BMW
To fix DTC P121C on a BMW, you can try the following solutions:
- Repair or replace any damaged wiring or connectors in the NOx sensor heater control circuit
- Replace the faulty NOx sensor heater with a new one
- If the ECU is found to be faulty, reprogram or replace it as necessary
- Clear the fault code and perform a test drive to ensure the issue is resolved
How to erase DTC P121C on BMW
To erase DTC P121C on a BMW, you can use a diagnostic scanner to clear the fault code from the ECU’s memory. After making the necessary repairs and confirming that the issue has been resolved, you can reset the MIL (Check Engine Light) and ensure that the fault code does not reappear during subsequent driving cycles.
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.