P0556Brake Booster Pressure Sensor Circuit Range/Performance
- 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. P0556 means the signal is valid but implausible. GM compares it with intake vacuum (MAP) with the throttle nearly closed for over 3 s, filtered, type B with two trips. VW and Porsche also check the electric vacuum pump with it – Porsche compares the pressure at wake-up and 1.5 s later – so P0556 can also mean a weak pump or a leak. VW fixed false setting on the 2016–17 Jetta 1.4 T by software.
- What you may notice
- Check engine light and/or brake booster warning
- Stop-start not working
- Hard brake pedal with real vacuum loss
- Likely causes
- LikelyLeaking or kinked vacuum line or faulty check valve
- PossibleSensor stuck or drifting
- PossibleElectric vacuum pump or its relay weak (hybrid, Porsche, turbo DI)
- RareModule software (false setting)
- RareBooster diaphragm leaking
- 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.