Damaged, corroded or loose wiring or connector at the brake booster pressure sensor; Faulty brake booster pressure sensor; Vacuum leak in the servo, check valve or vacuum hose giving an implausible reading; Weak vacuum supply, such as a failing vacuum pump on vehicles that have one; Open circuit, short to earth or short to supply in the sensor signal, reference or earth wires; Fault in the control unit that reads the sensor.

P0555

Brake Booster Pressure Sensor Circuit.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
55: FaultThe specific fault in that area

What it means

P0555 is the SAE J2012 generic code for a fault in the brake booster pressure sensor circuit. The sensor measures vacuum in the brake servo so the control unit can judge how much assistance the brakes have. The code sets when the signal voltage is outside the expected range, is implausible compared with engine load or manifold pressure, or is erratic or missing.

Symptoms

Brake warning light or engine management light on
Hard or heavy brake pedal feel
Longer braking distances than normal
Hissing noise from the servo area when pressing the pedal
Rough idle or stalling if there is a vacuum leak
Stop-start system disabled or behaving oddly

Possible causes

Damaged, corroded or loose wiring or connector at the brake booster pressure sensorlikely
Faulty brake booster pressure sensorlikely
Vacuum leak in the servo, check valve or vacuum hose giving an implausible readingpossible
Weak vacuum supply, such as a failing vacuum pump on vehicles that have onepossible
Open circuit, short to earth or short to supply in the sensor signal, reference or earth wirespossible
Fault in the control unit that reads the sensorrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, then check for other brake, vacuum or engine codes
Visually inspect the sensor, its connector and the wiring for damage, corrosion, chafing, moisture and poor pin tension
Inspect the vacuum hose, check valve and servo connection for splits, loose clips and perrishing; listen for hissing at the pedal
Check the live sensor data with the engine off and running and see if it changes sensibly when the pedal is pressed and released
Measure the sensor reference voltage, earth and signal wire against the wiring diagram for the vehicle
Test the vacuum at the servo against the manufacturer's specification, including the vacuum pump where fitted
Check the wiring for continuity and shorts between the sensor and control unit before condemning any component
Clear the code after repair and road test to confirm it does not return

How to fix

Repair or replace damaged wiring and clean or replace the faulty connector
Replace the brake booster pressure sensor if it fails electrical or live data checks
Replace split or leaking vacuum hoses, a faulty check valve or a leaking servo
Repair or replace a weak vacuum pump where fitted
Repair circuit faults found between the sensor and control unit, and only then consider the control unit if all else checks out

Can I keep driving?

High severity

Braking assistance may be reduced or unreliable, so avoid driving until the fault has been checked. If the pedal feels hard or the brake warning light is on, do not drive the car and have it recovered to a workshop.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.