Chassis, generic

C054C Vacuum Sensor A Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Vacuum sensor A reports a voltage above its upper clamp. HELLA's booster sensor never exceeds 4.8 V when intact, even at full vacuum, so a higher reading indicates a signal shorted to the 5-V supply or to battery voltage, an open ground, or an internal defect. On a characteristic where more volts mean more vacuum, such a fault pretends a deep vacuum that may not exist; that is the riskier direction, because the electric pump could stay off. Brake units therefore check the circuit continuously; the 2023 Mitsubishi Outlander PHEV reports a shorted vacuum sensor circuit in at most one second and suspends brake assist. Bosch describes the sensor as the input for pump control and stop-start. No maker documents C054C publicly. C054B is the low counterpart, C0550 the same fault on sensor B.

Likely causes

Signal line shorted to supply or battery voltage
Sensor ground interrupted
Sensor failed with output stuck high

Symptoms

  • Brake assist warning on
  • Harder brake pedal if the booster really runs short of vacuum

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–250
Time0.2–1.5 h

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

Parts involved

vacuum sensor asensor wiring

Related codes

C0549C054AC054BC0550

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