Chassis, generic

C056A Brake Booster Pressure Sensor Power Supply Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Open or shorted 5 V supply wire to the sensor
Another sensor on the same reference pulling the supply down
Corroded sensor connector
Faulty 5 V regulator in the control module

Symptoms

  • Brake or stability warning, often with further sensor codes
  • Brake assist or electric vacuum pump control affected
  • Stop/start inactive on some cars

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€30–400
Time0.5–2 h

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

Parts involved

brake booster pressure sensorsensor supply

Related codes

C0547C0548C0560C056BP0556

References: fordservicecontent.com, hella.com, bosch-mobility.com.