P0558

What it means

P0558 is the generic code for a high signal from the brake booster pressure sensor circuit. The control unit saw the sensor's signal voltage sit above its expected range, which usually points to an open circuit, a short to voltage or a faulty sensor. The sensor monitors vacuum in the brake servo, and the exact layout and how the system uses this signal depends on the model.

Symptoms

• Warning light on, which may be the engine light or a brake-related warning depending on the model
• Hard or heavy brake pedal feel
• Brake pedal feels different from normal, such as unusually firm or inconsistent
• Rough idle or poor idle control on some models
• Reduced engine braking or start-stop system disabled on some vehicles
• No noticeable change in driving other than the stored fault

Possible causes

• Faulty brake booster pressure sensor giving a false high readinglikely
• Wiring fault such as an open circuit in the signal or ground wire, or a short to voltage on the signal wirelikely
• Corroded, loose or damaged connector at the sensor or control unitlikely
• Genuine low vacuum in the brake servo (leaking vacuum hose, non-return valve or servo, or failing vacuum pump on models with one)possible
• Fault in the sensor's reference voltage supply or ground shared with other sensorspossible
• Faulty control unit or outdated software where a known issue is documented by the manufacturerrare

How to diagnose

1. Read all stored codes and freeze frame data, and note whether other vacuum, brake or sensor supply codes are present.
2. Check the brake pedal feel with the engine off and on, and listen for hissing from the servo or vacuum hose.
3. Inspect the sensor, its connector and the wiring for damage, chafing, water ingress, corrosion and bent or pushed-back pins.
4. Inspect the vacuum hose, non-return valve and servo connection for splits, loose fittings and leaks, and check the vacuum pump where fitted.
5. With the ignition on, check live data for the sensor reading and compare it against the expected value for the conditions, and check how it responds when the brake pedal is pumped.
6. Measure the sensor's reference supply and ground at the connector against the manufacturer's specification.
7. Check the signal wire for a short to voltage or an open circuit, with the connector unplugged and the control unit isolated as the procedure requires.
8. Check for relevant technical bulletins or software updates for the model before condemning the control unit.

How to fix

• Replace the brake booster pressure sensor if it is confirmed faulty or reads incorrectly against a known good reference.
• Repair or replace damaged wiring, and clean or replace corroded or damaged connector terminals.
• Repair vacuum leaks by replacing split hoses, a faulty non-return valve or a leaking servo as diagnosed.
• Repair or replace the vacuum pump on models that use one if it fails to produce adequate vacuum.
• Restore a correct reference supply or ground by repairing the fault in the shared circuit.
• Update the control unit software where a manufacturer update addresses the fault, and replace the unit only after all other causes are excluded.

Can I keep driving?

Nearby codes

• P0557GenericBrake Booster Pressure Sensor Circuit Low
• P0559GenericBrake Booster Pressure Sensor Circuit Intermittent