Chassis, generic

C0547 Vacuum Sensor Supply Voltage Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Fault in the feed circuit powering the vacuum sensor on the brake booster, usually an open or a short on the regulated supply. Such sensors need a stable 5 V: HELLA specifies 4.5 to 5.5 V for its three-pin vacuum sensor (output, ground, supply), whose analogue signal tells the brake control unit when to run the electric vacuum pump. Bosch describes the same sensor as the basis for pump control, stop-start and ESP assistance. A Saab 9-5 brake module shows how a supply is policed on a brake sensor: outside 4.4 to 5.6 V lasting 0.06 s is a fault. No maker documents C0547 publicly. Without valid supply the vacuum value is lost, so assist functions and an electric pump may run on fallback. C0548 is the narrower case of a supply that is merely too low.

Likely causes

Supply wire or connector pin interrupted
Supply line shorted to ground or another circuit
Vacuum sensor shorting the supply internally

Symptoms

  • Brake system or ESC warning shown
  • Stop-start inactive or electric vacuum pump running constantly

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–300
Time0.3–2 h

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

Parts involved

vacuum sensorsensor supply

Related codes

C0548C0549C054DP0641

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