C056ABrake Booster Pressure Sensor Power Supply Circuit
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- Pressure sensors in the brake system are ratiometric parts fed with 5 V from the control module; HELLA's booster vacuum sensor, for example, is specified for 4.5–5.5 V and answers with 0.5–4.5 V. If that supply is missing or out of range, every reading is wrong, so C056A is checked before the sensor signals are judged. Ford's 2015–2019 hybrids use C056A exactly this way: the missing-calibration and erratic checks of the brake pressure sensors (C0560, C056B) only run when no C056A supply fault is present. No maker publishes a C056A threshold. Bosch notes the booster vacuum signal also governs the electric vacuum pump and start/stop. Expect brake assist and stability functions to be limited.
- What you may notice
- Brake or stability warning, often with further sensor codes
- Brake assist or electric vacuum pump control affected
- Stop/start inactive on some cars
- Likely causes
- LikelyOpen or shorted 5 V supply wire to the sensor
- PossibleAnother sensor on the same reference pulling the supply down
- PossibleCorroded sensor connector
- RareFaulty 5 V regulator in the control module
- Repair
- Medium · Usually a job for a workshop.Typical cost: €30 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.