P0555: Brake Booster Pressure Sensor Circuit
What to do
Test the brakes carefully somewhere safe before driving normally. With the engine running, the pedal should feel normal; if it is unusually hard, stopping distances will be much longer than you expect and the car should not be driven far. If the pedal feels normal, this is more likely to be the sensor than the vacuum supply, but it should be confirmed rather than assumed.
What this code means
A circuit fault on the brake booster pressure sensor. The booster multiplies pedal effort using vacuum — on a petrol engine drawn from the intake manifold, and on a diesel or a turbocharged petrol from a dedicated pump, since neither produces reliable manifold vacuum. The sensor lets the module confirm sufficient vacuum is available, and on many vehicles run that pump on demand.
The reason this ranks above the other sensor codes in the block is what happens if the vacuum is genuinely absent rather than merely unmeasured. The brakes still work without assistance, but the pedal becomes very hard and requires far more effort for the same retardation — which is a serious surprise if it is discovered during an emergency stop rather than in a car park.
Likely causes
Start here
- Faulty brake booster pressure sensor · moderate
- Corroded or loose connector · easy
Less common
- Faulty vacuum pump · moderate
- Disconnected or leaking vacuum hose · easy
- Leaking brake booster diaphragm · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0555.