P0555Generic code

P0555 Code: Brake Booster Pressure Sensor Circuit

The P0555 code means the computer found an electrical fault in the brake booster pressure sensor circuit. The main risk is a possible loss of brake assist. A damaged or corroded connector is the most common cause, but always check that the brake pedal still has normal assist.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$40 to $300
Difficulty
Medium
System
Chassis, Brakes and Suspension
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0555 code means

On vehicles with an electric vacuum pump, or with engines that make little vacuum (direct injection, turbo, hybrids), a sensor measures the brake booster vacuum so the pump can be turned on or the engine adjusted.

The sensor gets a 5 V reference and a ground from the computer and returns a signal between about 0.5 and 4.5 V. A circuit fault, which is what the P0555 code reports, can come from the sensor, from the wiring or from the supply.

Without this signal, the computer does not know whether there is enough brake assist. It may run the vacuum pump continuously or turn on a brake warning. Always check that the brake pedal has normal assist.

Always start with the simple things: the fuse, the relay and the connector. Then check the supply, the ground and the signal with the component plugged in (using back-probes), and finally the continuity of each wire all the way to the computer. Only replace the component if all of that checks out.

P0555 code symptoms

  • Check engine light on.
  • Possible loss of brake assist.
  • Hard brake pedal.
  • Vacuum pump running continuously.
  • Brake warning.

Likely causes of the P0555 code

  1. Damaged or corroded connector. The most frequent cause.
  2. Wiring cut or shorted between the sensor and the computer.
  3. Failed sensor. Open or shorted inside.
  4. Missing supply reference. Check whether other sensors are also failing.
  5. Computer. Uncommon, so rule out everything above first.

How to diagnose the P0555 code step by step

  1. Read the sensor value on the scan tool and compare it with what you expect.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check the supply and ground with the key on: the reference should be correct, with less than 0.1 V of voltage drop on the ground.
  4. Measure the signal with the connector plugged in and watch whether it changes with the condition.
  5. Do a wiggle test on the harness with the scan tool in graph mode.
  6. Check the continuity of each wire to the computer (under 1 ohm).

How to fix the P0555 code

  • Repair the connector or the wiring.
  • Replace the sensor if the tests confirm it is bad.
  • Correct the real condition if there is one.
  • Clear the codes and verify with a road test.

Technical reference data

  • 5 V reference, ground and a signal proportional to the vacuum.
  • These values are a general guide: check the manufacturer data for your vehicle.

Brand-specific notes

This code is usual on vehicles that rely on an electric vacuum pump or that make little engine vacuum.

P0555 on BMW

Usual on BMW vehicles.

P0555 on Volkswagen

Usual on Volkswagen vehicles.

P0555 on Ford EcoBoost

Usual on Ford EcoBoost engines.

P0555 on Hybrids

Usual on hybrid vehicles.

Frequently asked questions about P0555

Can I drive with a P0555 code?
With great caution. If the brake pedal is hard, stopping takes more force, so have it checked as soon as you can.
What does the P0555 code mean?
It is a generic OBD2 code that means the computer found an electrical fault in the brake booster pressure sensor circuit. The result can be a loss of brake assist.
Do I have to replace the sensor?
Only if the tests confirm it. The connector and the wiring fail just as often.
What does the brake booster pressure sensor do?
On vehicles with an electric vacuum pump, or with engines that make little vacuum (direct injection, turbo, hybrids), a sensor measures the brake booster vacuum so the pump can be turned on or the engine adjusted.
How much does it cost to fix P0555?
As a rough guide, between $40 and $300. A connector repair is at the low end, and a new sensor with labor is at the high end.
Will a P0555 code clear itself?
Only if the fault was temporary. A corroded connector or a damaged wire will bring the P0555 code back, so find the cause before you clear it.
What is the most common cause of P0555?
A damaged or corroded connector. Wiring that is cut or shorted and a failed sensor come next.

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