What does it mean?
C1187 is a Chassis (ABS, traction control, steering) fault code. It indicates: ABS Hydraulic Valve Power Relay Circuit Short to Battery . 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 and stability control warning lamps on, sometimes with the red brake warning lamp
- ABS does not intervene under hard braking and the pedal does not pulse
- Quiet humming from the ABS hydraulic unit after the ignition has been switched off
- Flat battery after the car has been left standing, or a parasitic drain measured at the battery
- ABS unit warm or hot to the touch when the car has not been driven recently
Likely causes
- Relay contacts stuck or welded together, so the valve supply is never switched off
- Insulation worn through between the relay circuit and an adjacent permanently live wire
- Corrosion or water inside the fuse and relay box creating a leakage path from a live terminal
- Relay of the wrong rating or type fitted, or fitted into a neighbouring slot by mistake
- Additional electrical equipment spliced into the ABS harness, feeding voltage back into the circuit
- Loom damage where it crosses the battery tray, the starter feed or a fuse box entry point
- Failed monitoring or driver stage inside the ABS control module
How to fix it
- Measure key-off current draw and check the hydraulic unit temperature after the car has stood; both point directly at a circuit that stays live
- Read all chassis codes at once; several short to battery codes together indicate one shared feed problem
- Remove the relay and test it off the car for stuck or welded contacts, and confirm the correct relay is in the correct slot
- Inspect the fuse and relay box for water ingress, corrosion and carbon tracking between adjacent terminals
- With the relay out and the module unplugged, look for voltage on the control wire; any voltage confirms an unwanted feed
- Follow the harness looking for chafe against live cables and inspect every non-factory splice in the engine bay
- Repair the wiring or replace the faulty relay, and only consider ABS module repair once the external circuit is confirmed clean