P0555 to P0559: brake booster pressure sensor
The sensor that measures vacuum or pressure in the brake booster has a circuit fault or an implausible, low, high or intermittent signal.
SeverityHighCarrying on can cause expensive damage, so deal with it now.
Can you keep driving?Only as far as the workshopWhat does P0555 mean?
The brake booster uses engine vacuum, or a vacuum pump on many diesels and turbo engines, to multiply the force of your foot on the pedal. Some cars measure that vacuum so the engine computer can keep it high enough, for example by closing the throttle a little or running the vacuum pump, and so it can warn when braking assistance is low. A sensor fault means the computer cannot confirm that assistance; a real loss of vacuum means a much harder brake pedal.
What causes P0555?
- A failed booster pressure sensor or a damaged wire to it
- A cracked vacuum hose or a failed check valve on the booster
- A failing vacuum pump, on cars that have one
- A leaking brake booster diaphragm
What to check first for P0555
- With the engine off, press the brake pedal several times, then start the engine: the pedal should sink slightly
- Note whether the pedal feels harder than usual, or a hiss comes from under the dash when braking
- Inspect the vacuum hose and check valve between the engine and the booster
- Compare the booster pressure reading with the engine off and running on a scan tool
Can you drive with P0555?
If the brake pedal feels normal, drive gently to a workshop and leave more distance to brake. If the pedal is hard or you hear a hiss when braking, do not drive; have the car towed, because stopping will take much more force.
Since May 2018 an engine warning light that stays on is a major defect at the MOT, so the car fails until the fault is fixed.
Codes on this page
- P0555Brake Booster Pressure Sensor Circuit
- P0556Brake Booster Pressure Sensor Circuit Range/Performance
- P0557Brake Booster Pressure Sensor Circuit Low Input
- P0558Brake Booster Pressure Sensor Circuit High Input
- P0559Brake Booster Pressure Sensor Circuit Intermittent
Related codes
Checked on · Rafael Soares
These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.
