What does it mean?
C1251 is a Chassis (ABS, traction control, steering) fault code. It indicates: Brake Fluid Pressure Sensor Circuit Failure . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- ABS, stability and brake warning lamps on together
- Stability control, hill-hold and brake assist unavailable
- Brake pedal feel different from normal, and ABS may cut in early or late
- Pressure value on the scan tool stuck at zero, pegged high or jumping around
- Fault stores again on the first firm brake application after clearing
- Damp area or fluid staining around the sensor on the hydraulic unit
Likely causes
- Sensor failed internally or drifted so it no longer matches real line pressure
- Open, shorted or high resistance signal wire, or a missing reference voltage
- Poor sensor ground return
- Corroded connector, or brake fluid weeping past the sensor seal into the plug
- Sensor zero point not learned after brake, sensor or hydraulic unit work
- Air in the brake system so pressure does not rise as the module expects
- Module input circuit failure
How to fix it
- Read the live pressure value with the pedal released; it should be at or very close to zero
- Apply the pedal progressively and confirm the value climbs smoothly and falls back again
- Check the reference voltage and ground at the sensor connector, then check the signal wire for continuity and shorts
- Inspect the connector for corrosion and for brake fluid that has crept in from a leaking seal
- Bleed the brake system and confirm a firm pedal before judging the sensor
- Carry out the zero point learn routine with the scan tool
- Replace the sensor, or the hydraulic unit where the sensor is integrated, then bleed, relearn and road-test