C0549Vacuum Sensor A Circuit/Open
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- General circuit fault of vacuum sensor A, usually a broken or disconnected signal, ground or feed line. The sensor measures the vacuum in the brake booster; Bosch notes that its value lets the system run the electric vacuum pump, permits engine stop-start and supports ESP functions. Mitsubishi shows how a brake unit watches it on the 2023 Outlander PHEV: with power on and normal supply, an open or a short in the brake vacuum sensor circuit, or signal noise, is detected within a second and stored as C1073, after which brake assist is suspended; Mitsubishi does not map that fault to an SAE code. Which physical sensor is called A is manufacturer-specific, and no maker documents C0549 publicly. C054A to C054C cover plausibility, low and high signal.
- What you may notice
- Brake assist warning or ABS lamp on
- Stop-start no longer switching off the engine
- Likely causes
- LikelySensor plug loose or not latched after work in the engine bay
- PossibleBroken signal, ground or supply wire
- RareInternal open in the vacuum sensor
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.