What it means
A general circuit fault is detected on the brake booster pressure sensor - the ECU cannot determine vacuum reserve in the booster, which limits the safe operation of stop-start, regenerative-braking blending, and electric vacuum pump control.
At a glance
- Usually lights the check-engine light
How it works
The brake booster pressure sensor reports the booster’s pressure or vacuum condition to the control module. P0555 indicates a general electrical fault in that sensor circuit, so systems that depend on the reading, such as stop-start or an electric vacuum pump, may be disabled or respond incorrectly.
Common causes
Most likely first.
- Brake booster pressure sensor failure
- Open or short in sensor wiring
- Loose, damaged, or corroded connector
Symptoms
- Check-engine light on
- Stop-start or brake-assist features may be disabled
How to diagnose it
- Read freeze-frame data and check for messages or stored faults related to brake assist, stop-start, or an electric vacuum pump.
- With the vehicle safely stationary, check whether the brake pedal feels unusually hard or braking assistance has changed.
- Inspect the brake booster pressure sensor connector and wiring for loose terminals, corrosion, fluid contamination, or damage.
- Check the sensor circuit's power, ground, and signal against the wiring information and manufacturer's specification.
- Monitor the pressure-sensor signal and test the sensor and circuit to determine whether the fault is electrical or within the sensor.
Common fixes
- Reconnect and secure a loose brake booster pressure sensor connector.
- Clean corroded terminals and repair damaged sensor wiring.
- Restore a faulty circuit power, ground, or signal connection.
- Replace a brake booster pressure sensor that fails the specified circuit test.
Can I keep driving?
If the brake pedal feels hard, braking assistance changes, or a brake warning appears, stop driving and arrange inspection because stopping distance may increase. If braking feels normal, drive only cautiously to have the fault checked; stop-start or related assist features may be unavailable.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.