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DTC codes / C05xx · Brakes, steering and suspension / C056F

C056FBrake Booster Travel Sensor Circuit Low

C056F indicates that the brake booster travel sensor circuit is reporting a voltage lower than the manufacturer's expected range, which the control module interprets as a short to ground or an open circuit. The sensor monitors the position of the brake booster pushrod to help the system determine how much assist is being applied and to support functions such as brake assist and hill hold.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • Illumination of the brake system warning light, often accompanied by the traction control or stability control light
  • A stored code in the anti-lock brake system (ABS) module with no noticeable change in brake pedal feel
  • Reduced or disabled brake assist feature, requiring more pedal effort during hard stops
  • Intermittent operation of hill start assist or electronic parking brake functions
  • Often no symptoms besides the warning light, especially if the sensor fails only at certain temperatures

Common causes, most likely first

  1. Damaged or chafed wiring harness between the brake booster travel sensor and the ABS control module
  2. Corroded or loose electrical connector at the sensor or at the control module
  3. Failed brake booster travel sensor due to internal wear or contamination
  4. Water intrusion into the sensor connector causing a short to ground
  5. Poor ground connection for the sensor circuit
  6. Faulty ABS control module internal circuitry (less common)

How to diagnose and fix it

  1. Inspect the sensor connector and wiring for corrosion, chafing, or loose pins, and repair as needed
  2. Check the sensor's ground circuit for excessive resistance and clean or tighten the ground point
  3. Measure the sensor signal voltage with a scan tool while slowly moving the brake pedal to compare against the manufacturer's specification
  4. Perform a voltage drop test on the signal and ground wires to rule out high resistance in the harness
  5. Replace the brake booster travel sensor if voltage readings are outside the specified range or erratic
  6. Clear the code and perform a road test to verify the repair, including a calibration or relearn procedure if required

What the brake booster travel sensor code hides

  • A low voltage code often results from a simple unplugged or partially seated connector after recent brake or suspension work, so always check connector engagement before condemning the sensor.
  • The brake booster travel sensor is sometimes integrated into the brake booster assembly on certain vehicles, making replacement more involved than a stand-alone sensor.
  • A weak battery or charging system can cause the ABS module to log a low voltage code for the sensor circuit even when the sensor itself is healthy.
  • The code can be set by a momentary short to ground during driving over rough roads, so intermittent faults may require wiggle testing the harness while monitoring live data.
  • Do not confuse this code with a brake pedal position sensor code; the booster travel sensor measures pushrod movement inside the booster, not pedal arm rotation.

Can I keep driving with C056F?

The vehicle remains safe to drive under normal conditions because the base hydraulic brakes are unaffected, but brake assist and stability functions may be reduced. Avoid hard braking or towing until the fault is repaired, and have the system diagnosed promptly to restore full safety features.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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