What does it mean?
C1091 is a Chassis (ABS, traction control, steering) fault code. It indicates: ABS Brake Lamp Control Circuit High .
Symptoms
- ABS and stability control warning lamps on
- Brake lights stay on with the pedal released, or work erratically
- Cruise control refuses to engage or drops out
- Shifter may resist coming out of Park on vehicles with a brake interlock
- Brake lamp fuse blows repeatedly
- Battery drains overnight when the lamps stay lit
Likely causes
- Brake lamp control wire chafed against a live circuit and shorted to battery voltage
- Failed or misadjusted brake lamp switch feeding voltage constantly
- Brake lamp relay with stuck or welded contacts
- Corroded or water damaged connector at the switch, the lamp cluster or the ABS module
- Open ground on the lamp circuit, which makes the module read a floating high signal
- Incorrect bulbs or a poorly installed trailer wiring kit back-feeding the circuit
- Failed output driver inside the ABS control module
How to fix it
- Inspect all brake bulbs, sockets and the fuse for corrosion or the wrong bulb type
- Watch the brake switch signal in live data while an assistant works the pedal
- Check the brake pedal switch adjustment and the pedal stop pad, which often crumbles
- Disconnect the brake switch and check whether voltage is still present on the control wire
- Inspect the harness where it passes the pedal bracket and behind the tail lamps for chafing
- Disconnect any aftermarket trailer or lighting wiring and retest
- Repair or replace the switch, relay or harness section, and only then consider the ABS module