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P0555 – Brake Booster Pressure Sensor Circuit (OBD2)

P0555 means "Brake Booster Pressure Sensor Circuit". The control unit has detected a fault in the electrical circuit of the brake booster pressure sensor: the signal or control current is missing or outside the expected window. The code does not say whether the value is too high or too low, so the wiring and the component itself both have to be checked.

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P0555 quick summary

Fault codeP0555
MeaningBrake Booster Pressure Sensor Circuit
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityMedium
Can I drive?Yes, if the brake pedal feels normal. If the pedal is hard and braking needs much more force, stop and have the car checked.
Repair cost€20 – €400

How the brake booster pressure sensor works

The brake booster pressure sensor measures the vacuum in the brake servo, so the engine control unit can ensure there is enough vacuum for braking assistance.

The brake booster uses engine vacuum (or a vacuum pump on diesels and some petrol engines) to multiply the force on the brake pedal. A pressure sensor on the booster tells the control unit how much vacuum is available. If it is too low, the control unit can change throttle or engine strategy, run an electric vacuum pump or prevent the start-stop system from switching off the engine.

Codes P0555–P0559 report circuit, range and intermittent faults of this sensor.

A faulty sensor can disable start-stop or cause warnings, but a real lack of vacuum makes the brake pedal hard – which is a safety issue.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16939 (P0555). Both numbers mean the same fault.

Symptoms of P0555

  • Check Engine or brake warning
  • Start-stop system not working
  • Hard brake pedal (real vacuum problem)
  • Hissing near the brake booster
  • Often no other symptoms

Most common causes of P0555 (most likely first)

Mechanic's Pro Tip

If start-stop no longer works, the brake booster sensor is one of the less obvious reasons – check its value in live data.

  1. 1.Damaged wire or loose, corroded connector at the brake booster pressure sensor

    Most likely

    Green or white corrosion, pushed-back pins and chafed insulation near hot or moving parts are the most common findings.

  2. 2.Faulty brake booster pressure sensor

    An internal break or short in the component itself.

  3. 3.Blown fuse or missing supply voltage

    If several codes appeared at the same time, check the shared fuse, relay or ground point first.

  4. 4.Vacuum leak in the booster hose or check valve

  5. 5.Weak vacuum pump

  6. 6.Brake booster diaphragm leak

Step-by-step diagnostic guide

  1. 1

    Check the brake pedal

    With the engine running, check that the brake pedal is soft and assisted.

  2. 2

    Check the circuit with a multimeter

    With the ignition off, unplug the brake booster pressure sensor and the control unit connector (or back-probe), then check each wire between them for continuity and for shorts to ground and to battery voltage. Compare the component's resistance or supply voltage with the value in the repair manual.

    Multimeter: Wire continuity: below about 1 Ω. Wire to ground with both connectors unplugged: no continuity. Supply/reference with ignition on: usually 5 V for sensors, battery voltage for actuators.

  3. 3

    Read codes and booster vacuum

    Read all codes and watch the booster pressure in live data.

  4. 4

    Check hoses and check valve

    Check the vacuum hose and one-way valve for leaks.

  5. 5

    Measure vacuum

    Measure the vacuum with a gauge and compare with the sensor reading.

    Multimeter: Typical booster vacuum: about 0.6–0.8 bar below atmospheric at idle.

  6. 6

    Replace and verify

    Replace the sensor or fix the vacuum leak and check the brakes.

Frequently asked questions

Can I keep driving with P0555?

Yes, if the brake pedal feels normal. If the pedal is hard and braking needs much more force, stop and have the car checked.

How much does it cost to fix P0555?

Typical repair costs are 20 € – 400 €, depending on the cause and the vehicle. The most common fixes are: damaged wire or loose, corroded connector at the brake booster pressure sensor; faulty brake booster pressure sensor; blown fuse or missing supply voltage. Always confirm the cause with the tests above before buying parts.

Is a brake booster sensor code dangerous?

The sensor fault itself is not, but a real vacuum loss makes braking harder – check the pedal feel.

Why does it affect start-stop?

The engine must keep running if there is not enough vacuum for the brakes.

What is the difference between P0555 and similar codes?

P0555 belongs to a group of codes for the same component that differ in the type or location of the fault: C0567 – Brake Booster Solenoid Circuit Low; C0568 – Brake Booster Solenoid Circuit High; C0569 – Brake Booster Solenoid Performance; P0556 – Brake Booster Pressure Sensor Circuit Range/Performance; P0557 – Brake Booster Pressure Sensor Circuit Low Input; P0558 – Brake Booster Pressure Sensor Circuit High Input. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.