P0555: Brake booster pressure sensor circuit fault

Brake booster pressure sensor circuit malfunction

Severity: Inspect soon

The code points at the sensor that tells the computer how much vacuum or pressure is assisting the brake pedal. In the Ford F-150 complaint a stiff brake pedal came with the code, so treat it as a braking fault.

It gets more serious if:

Stop: Stop driving if the brake pedal is hard to press or the car is slow to stop; get it towed rather than driven.

Safety-critical system: explanation only, no DIY steps. Source: how we rate severity

P0555 in short

P0555 means the computer sees a fault in the brake booster pressure sensor circuit, the sensor that monitors the assist behind the brake pedal. Likely causes are wiring, a poor connection, the sensor, or the control module. A stiff pedal makes this a braking problem, so have it inspected promptly.

The brake booster uses engine vacuum, or a pump on some engines, to make the pedal easy to press. A pressure sensor reports that assist to the computer, which uses it for brake and stability functions.

P0555 is stored when the computer judges the sensor circuit to be faulty. TroubleCodes.net lists wiring, a poor connection, the sensor and the control module as the probable causes. It is a circuit code, not proof that the booster itself has failed.

In one Ford F-150 complaint the dealer read P0555 together with P0556 (range or performance of the same sensor) after the pedal went stiff. Because brakes are involved, diagnosis belongs with a shop.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

Cause 1: Wiring or connector fault in the sensor circuit
Common general cause
Why it ranks here
TroubleCodes.net lists wiring and poor connections first for this circuit code, and circuit codes are most often caused by the wiring they travel through.
What would change this
Rises if the connector is loose, corroded or the harness is damaged near the booster. Falls if the circuit tests normal.
Cause 2: Brake booster pressure sensor
Common general cause
Why it ranks here
The sensor itself is listed as a probable cause. The Ford complaint shows P0555 and P0556 together, which fits a sensor that is not reporting plausible values.
What would change this
Rises if wiring tests good and the sensor reading does not follow the pedal. Falls if the reading is plausible and steady.
Cause 3: Engine or brake control module
Possible — needs testing
Why it ranks here
The control module is listed last by TroubleCodes.net. It is rare compared with the wiring and the sensor, so it ranks last until those are cleared.
What would change this
Rises only after the wiring and sensor are both proven good. Falls if replacing the sensor or repairing the wiring clears the code.
How to test the engine control module (ecm / pcm)

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: Read all stored codes and note whether P0556 or other brake or stability codes are present with P0555.
Low riskTool: OBD-II scan tool
- IfP0555 appears with P0556
  It meansThe same sensor is being flagged for a circuit fault and for implausible readings, which points to the sensor or its wiring.
  Go to step 2
- IfP0555 is stored alone and the pedal feels normal
  It meansStill have the brake system checked soon, because the sensor feeds braking functions.
  Go to step 2
Step 2: Have a shop inspect the sensor wiring, connector and sensor and check the pedal assist.
Best left to a shopTool: scan tool with live data, multimeter
Warning:Brake system work affects your ability to stop. Do not disconnect brake parts or road-test a car with a stiff pedal; use a qualified shop.
- IfThe wiring or connector is damaged or loose
  It meansRepair it and retest the circuit.
  Points to: Wiring or connector fault in the sensor circuit
- IfThe wiring is good and the sensor reading is wrong
  It meansThe sensor is the likely fault.
  Points to: Brake booster pressure sensor
- IfWiring and sensor are both good
  It meansLook at the control module last.
  Points to: Engine or brake control module

Symptoms

Check engine light or brake warning message
Brake pedal harder to press than usual Gets more serious: stop and have it checked.
Longer stopping distance Gets more serious: stop and have it checked.

How to fix

This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.

Parts and cost context

Engine control module (ECM / PCM):A control module is the last item to suspect. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Ford

2017 · F-150
Supported by vehicle data
One 2017 F-150 complaint reports P0555 with P0556 and a stiff brake pedal. A single complaint, not a documented pattern.

All ABS, traction and stability control codes

P0555 questions

Is it safe to drive with P0555?

Not if the brake pedal feels hard or the car is slow to stop. The sensor affects brake assist, so have it inspected promptly.

Sources and review

ODI 11584044: 2017 Ford F-150, brake pedal stiff, P0555 and P0556 — NHTSA Office of Defects Investigation (consumer complaint)
P0555 trouble code definition — TroubleCodes.net

Last reviewed: October 16, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Inspect soon

Most likely causes

Cause 1: Wiring or connector fault in the sensor circuit

Cause 2: Brake booster pressure sensor

Cause 3: Engine or brake control module

What to test first

Step 1: Read all stored codes and note whether P0556 or other brake or stability codes are present with P0555.

Step 2: Have a shop inspect the sensor wiring, connector and sensor and check the pedal assist.