P0555 - Brake Booster Pressure Sensor Circuit
Last updated:
System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0555 is a generic OBD-II diagnostic trouble code (DTC) indicating that the Engine Control Module (ECM/PCM) has detected an electrical malfunction or signal fault within the Brake Booster Pressure Sensor circuit. This sensor monitors the vacuum level inside the brake booster to ensure adequate power assist is available for braking. This is critical for vehicles equipped with Start/Stop technology or hybrid drivetrains where the engine (the primary vacuum source) may be shut off. If the signal voltage remains outside the calibrated range (typically 0.5V to 4.5V) for a specified duration, the ECM triggers the DTC. This often leads to the deactivation of the Start/Stop system to maintain vacuum integrity via an auxiliary pump.
Possible Causes
Faulty Brake Booster Pressure Sensor
Damaged wiring or corrosion in the sensor connector
Vacuum leak in the booster or check valve affecting sensor readings
Internal fault in the Engine Control Module (ECM)
Symptoms
Recommended Solution
- STEP 1: Inspect the electrical connector at the brake booster for moisture or corrosion. Clean as necessary.
- STEP 2: Inspect vacuum lines leading to the brake booster for cracks or leaks.
- STEP 3: Measure the sensor supply voltage. It should have a 5V reference and a solid ground. Check signal wire voltage with ignition on; the value should fluctuate when the brake pedal is pumped.
- STEP 4: Use a scan tool to monitor Live Data. If the pressure value remains static despite pedal movement, replace the sensor.
- STEP 5: Clear DTCs and perform a road test to verify the fix.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
Do you also have
other fault codes?
See how P0555 connects with your other fault codes. Our advanced analysis tool identifies causal relationships and root causes directly.