P0557Brake Booster Pressure Sensor Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Needs a drive cycle to confirm a fix
- How the car detects it
- The brake booster pressure sensor (5 V reference, signal, ground) measures the vacuum in the brake booster. On direct-injection, turbo, stop-start and hybrid engines intake vacuum is scarce, so the engine module watches it and creates vacuum when needed – closing the throttle, suppressing engine stop or running an electric vacuum pump. That makes it an input to idle and throttle control. P0557 means the signal voltage is too low: GM 2018 below 5 % of the 5 V reference in 320 of 400 samples (about 5 s), GM 2006 below 0.04 V; type B, two trips. Typical are a signal shorted to ground or an open signal or 5 V line. As low voltage means plenty of vacuum, the module would wrongly assume enough – so it uses a substitute value.
- What you may notice
- Check engine light or brake booster warning
- Stop-start inactive
- Often no change in driving
- Likely causes
- LikelySignal line open or shorted to ground, connector loose or corroded
- Possible5 V reference open or shorted to ground
- PossibleSensor faulty internally
- RareEngine module
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.