P0555
Brake Booster Pressure Sensor Circuit
- Severity
- High
- Driving
- Drive only to a garage
A fault in the brake booster pressure sensor circuit. This sensor tells the module how much vacuum or pressure is available to assist the brakes. The circuit fault itself does not remove assistance - but the module can no longer confirm that assistance is there, and on vehicles that manage the vacuum pump from this reading, it may stop being maintained.
Possible causes
- CommonFailed brake booster pressure sensor
- CommonVacuum leak in the booster hose or its non-return valve
- CommonCorroded connector or damaged wiring
- PossibleFailed vacuum pump, on engines that use one
- PossibleFailed brake booster diaphragm
- PossibleLoss of reference voltage or earth
What you might notice
- Brake pedal harder than usual
- More pedal effort needed to stop
- Hissing from the pedal area
- Brake warning message
- Engine idle affected when braking
What to check, in order
- Test the pedal before driving. With the engine off, press the brake pedal several times to use up the stored vacuum, then start the engine with your foot on the pedal - it should sink slightly as assistance arrives. If it does not, assistance is genuinely missing.
- Check the booster vacuum hose and its non-return valve for splits and looseness.
- Inspect the sensor connector for corrosion and water.
- Check the reference voltage and earth at the sensor.
- On a diesel or a direct-injection petrol engine, check the vacuum pump - these engines make little vacuum of their own and depend on it.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Vehicle speed control, idle control and auxiliary inputs
P0500P0501P0502P0503P0504P0505P0506P0507P0508P0509P0510P0511P0512P0513P0514P0515P0516P0517P0518P0519P0520P0521P0522P0523P0524P0525P0526P0527P0528P0529P0530P0531P0532P0533P0534P0535P0536P0537P0538P0539P0540P0541P0542P0543P0544P0545P0546P0547P0548P0549P0550P0551P0552P0553P0554P0555P0556P0557P0558P0559P0560P0561P0562P0563P0564P0565P0566P0567P0568P0569P0570P0571P0572P0573P0574P0575P0576P0577P0578P0579P0580P0581P0582P0583P0584P0585P0586P0587P0588P0589P0590P0591P0592P0593P0594P0595P0596P0597P0598P0599