Chassis, generic

C054B Vacuum Sensor A Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

The signal of vacuum sensor A has fallen below the lowest voltage a working sensor can produce. In HELLA's design the output runs from 0.5 V at no vacuum to 4.5 V at −1000 hPa and is clamped to a 0.4–4.8 V band, so anything under that floor must be electrical: a grounded signal line, an absent 5-V feed or an internally failed sensor. Because low voltage in such a characteristic means little or no vacuum, the brake control unit cannot trust the value and may run the electric pump as a precaution or block functions that depend on it, which Bosch names as pump control, stop-start and ESP assistance. Mitsubishi detects short circuits on its brake vacuum sensor within a second. No maker documents C054B publicly. C054C is the high counterpart.

Likely causes

Signal wire shorted to ground
5-V supply to the sensor missing
Sensor failed with output stuck low

Symptoms

  • Brake assist or brake system warning lit
  • Electric vacuum pump running continuously

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

C0549C054AC054CC054FC0548

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