Chassis, generic

C0550 Vacuum Sensor B Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Vacuum sensor B puts out more voltage than its design permits. HELLA caps the output of its booster sensor at 4.8 V, with 4.5 V already standing for −1000 hPa, so anything above is a wiring or sensor fault: signal touching the supply or battery voltage, a broken ground return or a failed sensor. Because a high voltage simulates strong vacuum, the control unit must not rely on it for switching the electric vacuum pump; Bosch describes that pump control as the core job of the measurement. Mitsubishi's brake unit catches vacuum sensor shorts within a second and suspends brake assist. No maker documents C0550 with this meaning; one GM bulletin cites C0550 at a rear differential clutch module, a GM-specific use. C054F is the low counterpart, C054C the same fault on A.

Likely causes

Signal of sensor B shorted to supply or battery voltage
Ground return of sensor B broken
Sensor B stuck at high output

Symptoms

  • Brake assist or brake system warning on
  • Firm pedal possible if the pump is not switched on when needed

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

C054DC054EC054FC054C

References: hella.com, bosch-mobility.com, mitsubishitechinfo.com, static.nhtsa.gov.