What it means
Same as P0555 with intermittent or erratic signal. Boost control tracks commanded vs. actual manifold pressure; persistent deviation means wastegate, vanes, hose or actuator are not delivering the requested pressure.
At a glance
- Usually lights the check-engine light
How it works
The brake-booster pressure sensor reports pressure to the control module, which checks whether the signal changes consistently with operating conditions. P0559 sets when that signal is erratic or drops out intermittently, often from a loose connection or harness disturbed by vibration.
Common causes
Most likely first.
- Intermittent contact at connector
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
Symptoms
- Check-engine light may come on
- Cruise control may not engage or may disengage
- Brake assist warning may appear
- Brake pedal feel or assist may vary if booster pressure is affected
How to diagnose it
- Save freeze-frame data and review live brake-booster pressure for dropouts, noting whether they coincide with vibration or movement.
- Inspect the sensor connector for loose fit, corrosion, or damaged pins.
- Examine the harness routing for chafing or contact with vibrating or hot components.
- Check the signal, power, and ground circuits for intermittent opens or shorts while monitoring the reading, following the manufacturer's specifications.
- If the connections and wiring pass, test the pressure sensor against the manufacturer's specification.
Common fixes
- Secure a loose sensor connector and clean corroded contacts.
- Repair chafed or damaged wiring and secure it away from vibrating components.
- Repair an intermittent open or short in the sensor circuit.
- Replace the pressure sensor if it fails testing.
Can I keep driving?
Use caution because brake assist may vary and the pedal may become harder to press; avoid driving if pedal feel changes or a brake warning appears. Stop safely if braking effort increases.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.