P0559
Brake Booster Pressure Sensor Circuit Intermittent
Brake booster / sensors
Generic OBD-II
Medium
What it means
P0559 means the signal from the brake booster pressure sensor is cutting in and out. This sensor tells the ECM how much vacuum/pressure assist the brake booster has. The fault is usually a loose connector or chafed wire rather than the sensor itself. The brakes still work, but because it touches the brake system it is worth checking without delay.
Medium
Can I keep driving? Drivable, and the brakes still work mechanically, but pedal assist may occasionally feel harder than normal — get it checked promptly since it touches the brake system.
Common symptoms
What you'll notice
- Check-engine light on
- Brake pedal that occasionally feels harder or less assisted than usual
- Stop/start or brake-dependent features cutting out intermittently
- Fault that comes and goes rather than staying constant
Common causes
Most likely first
- Intermittent wiring fault or loose/corroded connector at the brake booster pressure sensor (most common for an intermittent code)Likely
- Failing brake booster pressure sensorCommon
- Chafed or pinched harness that shorts or opens as the car movesCommon
- Faulty engine control module (ECM), rareLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data to see when the dropout occurs, then wiggle-test the sensor connector and harness.
- Inspect the connector and wiring for corrosion, spread terminals, or chafing; clean and repair as needed.
- Check the sensor's reference voltage, ground, and signal against spec.
- If wiring is sound, replace the brake booster pressure sensor.
- Clear the code and road-test to confirm the intermittent fault is gone.
FAQ
Quick answers
Is it safe to drive with P0559?+
The brakes still function, but assist can feel inconsistent, so drive gently and get it diagnosed soon. If the pedal ever goes hard and stays hard, stop and have it checked immediately.
Can I just clear P0559?+
You can, but an intermittent wiring or sensor fault will set it again. Because it involves braking, it is worth tracing rather than just clearing.
Related codes
Often seen with P0559
Read & clear P0559 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX