C054AVacuum Sensor A Range/Performance
- Generic OBD-II code · Chassis
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- Vacuum sensor A delivers an in-range voltage that does not agree with what the booster should hold. Patents show the logic: GM compares booster vacuum with engine vacuum from the MAP sensor while the throttle is closed, because the two should track each other without braking, and flags a sensor biased high or low when the difference persists too long; Ford relies on the check valve and treats a booster pressure clearly above manifold pressure as sensor degradation. Mitsubishi's 2023 Outlander PHEV brake unit has a related check that faults a booster vacuum of about 0 kPa while the engine runs (C106D-01), though that may also mean a real leak. No maker documents C054A publicly; A-B assignment varies. Electrical faults are C0549, C054B and C054C.
- What you may notice
- Brake assist warning or reduced assist feel
- Electric vacuum pump running more often than normal
- Stop-start or cylinder deactivation inhibited
- Likely causes
- LikelyVacuum sensor drifted or contaminated (oil, moisture)
- PossibleReal leak in hose, check valve or booster making the reading look wrong
- RareFaulty comparison value, such as manifold pressure
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.