What does it mean?
C1237 is a Chassis (ABS, traction control, steering) fault code. It indicates: Primary Pressure Sensor-Signal .
Symptoms
- ABS, stability and brake warning lamps on together
- Stability control, hill-hold and brake assist disabled
- Brake pedal feel changes, and ABS may cut in earlier or later than usual
- On systems with an accumulator, the pump runs longer or more often than normal
- Pressure value on the scan tool stuck at zero, stuck high, or jumping
- Fault reappears on the first firm brake application after clearing
Likely causes
- Sensor internally failed or drifted so it no longer reports true line pressure
- Corroded connector, or brake fluid that has crept into the connector body
- Open or shorted signal wire, missing reference voltage or a bad sensor ground
- Zero point not learned after the sensor, master cylinder or hydraulic unit was disturbed
- Air trapped in the primary circuit so pressure does not build as expected
- Blocked port or restriction at the sensor location in the hydraulic unit
- Module input stage failure
How to fix it
- Read the live pressure value with the pedal released and again with the pedal held firmly, and judge whether it is plausible
- Compare with a second pressure sensor on the vehicle if one is fitted
- Check 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 ingress from a weeping sensor seal
- Bleed the brake system and confirm a firm pedal before judging the sensor
- Carry out the zero point learn procedure with the correct tool
- Replace the sensor, or the hydraulic unit where it cannot be separated, and repeat the learn and bleed procedure