Chassis, generic

C054F Vacuum Sensor B Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

The voltage from vacuum sensor B is lower than any value its characteristic allows. Taking HELLA's booster sensor as the reference, the output should never drop below 0.4 V, while 0.5 V corresponds to no vacuum at all; a reading underneath that is electrical rather than physical. A signal line grounded through chafing, a lost 5-V supply or a sensor with a dead output stage are the usual sources, and a low supply (C0548) can contribute. Mitsubishi's brake unit shows that short circuits on the brake vacuum sensor are caught within one second. Bosch lists pump control and stop-start among the functions fed by this measurement, so they fall back when it is lost. No maker documents C054F publicly. C0550 is the high fault, C054B the low fault of sensor A.

Likely causes

Signal wire of sensor B grounded
No 5-V feed at sensor B
Output stage of sensor B failed

Symptoms

  • Brake assist warning shown
  • Stop-start unavailable

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 bsensor wiring

Related codes

C054DC054EC0550C054BC0548

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