C056FBrake Booster Travel Sensor Circuit Low
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- The travel sensor tells the booster control how far its input side has moved. On older vacuum boosters it followed the movable wall; on Bosch's iBooster a differential travel sensor measures the offset between the pedal-driven input rod and the motor-driven booster body, and the controller works to bring that offset back to zero. C056F means the signal sits below its valid band – typically a short to ground, a lost sensor supply or an open reference. No maker publishes a C056F threshold; GM, for instance, files its pedal travel sensors as master cylinder piston position sensors (C05CC, C05CF). Without this input the module cuts or limits electric assist, so the pedal gets hard while the base brakes keep working.
- What you may notice
- Hard brake pedal with clearly higher pedal force
- Brake system or stability warning lamp and a message to service the brakes
- Brake assist, automatic emergency braking or regenerative braking unavailable
- Likely causes
- LikelyTravel sensor signal wire chafed through and shorted to ground
- PossibleMissing 5 V supply to the sensor, e.g. corroded connector pin at the booster
- PossibleInternal fault of the travel sensor, usually built into the booster assembly
- RareDefective sensor input stage in the booster control unit
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.