P0555 — Brake booster pressure sensor circuit problem

The code indicates an issue with the brake booster pressure sensor or its electrical circuit. This sensor monitors vacuum pressure in the brake booster, which helps provide power assist when braking. If the sensor or wiring is faulty, the car’s computer detects abnormal signals, triggering this code.

Common causes

The cause is almost always one of a few things. Here they are — P0555 rarely comes from anything outside this list:

• Faulty brake booster pressure sensor
• Damaged or corroded wiring/connectors
• Vacuum leak in brake booster system
• Faulty brake booster unit
• Malfunctioning powertrain control module (rare)

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Inspect and repair wiring/connectors to sensor
2. Check for vacuum leaks in brake booster system
3. Test and replace brake booster pressure sensor if faulty
4. Replace brake booster unit if sensor and wiring are good
5. Scan and reset codes after repairs

That is what holds for P0555 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.