What does it mean?
C1100 is a Chassis (ABS, traction control, steering) fault code. It indicates: ABS Hydraulic Valve Power 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
- ABS, stability control and sometimes the red brake lamp illuminate together
- No valve or relay click during the ignition on self test
- Conventional braking works, but ABS never engages during hard stops
- Traction control, hill hold and stability functions disabled
- Fault sets within seconds of turning the key on
- Code returns straight after clearing
Likely causes
- Failed valve power relay, usually integrated into the hydraulic control unit
- Burnt, loose or corroded terminals in the relay socket or the module connector
- Open or high resistance in the heavy feed that supplies the valve block
- Poor ABS module ground causing an unstable relay reference
- Low system voltage from a weak battery or charging fault when the relay is commanded
- Water ingress into the modulator connector after washing or driving through deep water
- Failed relay driver inside the ABS control module
How to fix it
- Check the ABS fuses and the relay, including the socket terminals for heat marks
- Measure battery voltage at the modulator connector with the key on
- Perform a voltage drop test on the valve block feed while the relay is commanded on
- Clean and tighten the ABS module ground and inspect the strap for corrosion
- Inspect the connector for moisture, then dry, clean and seal it
- Use the scan tool to command the relay and watch the reported status change
- Replace the hydraulic control unit or module assembly if the relay is internal and faulty, then code and bleed