P0559 Brake booster pressure sensor: signal drops out at times

By: Diagno editorial team · Updated: 2026-10-15

P0559 means: Brake booster pressure sensor: signal drops out at times. The computer found a fault in a sensor, valve or control circuit of this system. Drive gently and have the car checked soon. The repair usually costs about €40–300 in Estonia. The most common cause: connector loose, damp or corroded.

What it means

The computer found a fault in a sensor, valve or control circuit of this system. The signal drops out now and then. The most common cause is a loose connector or a chafed wire.

What you may notice

• Engine light on
• A function doesn't work properly

What could be wrong

1. 1Connector loose, damp or corroded
2. 2Wire broken or chafed
3. 3Faulty sensor or valve
4. 4Engine computer fault (rare)

Repair difficulty: Moderate

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Check the connector concerned and see whether the fault returns after clearing it. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the sensor or valve

Standard SAE description: Brake Booster Pressure Sensor Circuit Intermittent