What it means
The brake control module checks whether brake pressure sensor F has a valid calibration value. It sets this code when the calibration is missing or has not been learned.
At a glance
- Usually lights the ABS or stability-control warning light
How it works
Brake pressure sensor F provides a pressure reading to the brake control module for brake-system control. C05C4 is set when the module has no valid learned calibration for sensor F, often after the sensor or hydraulic control unit has been replaced or calibration was interrupted.
Common causes
Most likely first.
- Sensor calibration or relearn not completed
- Sensor or hydraulic control unit replaced without initialization
- Calibration interrupted or performed incorrectly
- Low system voltage during setup
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Scan the brake control module for related codes and check whether sensor F's calibration status is reported as missing.
- Review recent service history for replacement of sensor F or the hydraulic control unit, or an interrupted setup procedure.
- Check system voltage and inspect sensor F's connector and wiring for problems that could prevent calibration.
- If the circuit is sound, perform the manufacturer-specified calibration for pressure sensor F under its required conditions.
- Clear the code and confirm calibration status is valid and the code does not return.
Common fixes
- Complete the manufacturer-specified calibration or relearn for pressure sensor F.
- Restore stable system voltage and repeat calibration if low voltage interrupted setup.
- Reconnect or repair sensor F wiring or connector faults found during inspection.
- Replace a faulty sensor or address a hydraulic control unit fault only if testing prevents calibration from completing.
Can I keep driving?
ABS or stability control may be disabled while sensor F lacks a valid calibration. Have the calibration completed before relying on those systems, and stop if brake response or pedal feel is abnormal.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.