What does it mean?
C1252 is a Chassis (ABS, traction control, steering) fault code. It indicates: Brake Booster Pump Motor Relay 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
- Hard brake pedal because the booster pump never runs, or a pump that never stops
- Brake and ABS warning lamps on, often with a warning message
- No relay click at key-on when the pump would normally prime
- Battery drain if the relay stays closed with the vehicle parked
- Longer stopping distances and much higher pedal effort, so the vehicle is unsafe to drive
- Fuse blowing when the circuit is energised
Likely causes
- Relay coil open or shorted, or the contacts burnt and no longer making cleanly
- Contacts welded closed, so the pump keeps running whenever the battery is connected
- Corroded or heat damaged relay socket terminals in the fuse box
- Open or shorted control wire between the module and the relay coil
- Blown fuse feeding the relay contacts or the coil supply
- Poor ground for the relay coil circuit
- Relay driver stage inside the module failed
How to fix it
- Follow the system depressurisation procedure before working on the hydraulic side
- Locate the relay, remove it and test the coil resistance and the contact continuity, or substitute a known good relay
- Check the fuses feeding both the coil and the contact side
- Measure supply at the relay contacts and confirm the module switches the coil circuit when the pump is commanded
- Inspect the relay socket for melted plastic, corrosion and spread terminals
- Check the coil control wire for open circuit and shorts to ground or battery, and check the ground path
- Replace the relay, repair the wiring, and treat the module driver as the final candidate before re-testing pump operation