Chassis, generic

C056F Brake Booster Travel Sensor Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Travel sensor signal wire chafed through and shorted to ground
Missing 5 V supply to the sensor, e.g. corroded connector pin at the booster
Internal fault of the travel sensor, usually built into the booster assembly
Defective sensor input stage in the booster control unit

Symptoms

  • 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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–2,500
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

brake booster travel sensorsensor wiring

Related codes

C0570C0048C056DC056EC05CC

References: bosch-mobility.com, patents.google.com, patents.google.com, gsi.ext.gm.com.