What it means
The brake booster travel sensor signal is below the expected range. The module may not be able to determine booster travel correctly.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
The brake booster travel sensor tells the brake control module how far the booster mechanism moves. C056F sets when the sensor signal falls below the expected range, preventing the module from determining booster travel reliably.
Common causes
Most likely first.
- Signal wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Brake or ABS warning light
- Brake assist may be reduced, depending on the system
How to diagnose it
- Read brake-module freeze-frame and live booster-travel data to confirm the low reading and note when it occurs.
- Inspect the booster travel sensor connector and harness for corrosion, loose pins, or insulation rubbed through.
- Check the sensor signal wire for a short to ground, focusing on chafed areas near the booster and harness supports.
- Measure the sensor signal and related circuit continuity at the connector, comparing results with the manufacturer’s specification.
- If wiring and connections are sound, check booster travel sensor operation and its mounting for damage or movement.
Common fixes
- Repair loose or corroded terminals at the booster travel sensor connector.
- Repair a signal wire shorted to ground or damaged by chafing.
- Secure a loose sensor mounting if it is affecting the reading.
- Replace the booster travel sensor if its signal remains too low with a sound circuit.
Can I keep driving?
Brake assist may be reduced, so the pedal could require more effort; a warning light may also indicate limited ABS functions. Avoid driving if the pedal feels unusually hard or braking is impaired, and arrange prompt inspection.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.