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P codepowertrainHigh severity

P0558Brake Booster Pressure Sensor Circuit High Input

The brake booster pressure sensor signal voltage is stuck above its normal operating range, typically from an open circuit or a short to voltage.

Definition

The PCM monitors the brake booster pressure sensor signal and sets P0558 when the voltage exceeds the high threshold (commonly above about 4.8V), which indicates an open signal or ground circuit, a disconnected sensor, or a signal wire shorted to voltage. The MIL illuminates and booster vacuum monitoring is lost, so the PCM may run an auxiliary vacuum pump continuously or not at all, and a genuine loss of brake assist would go undetected. Brake pedal feel may remain normal until vacuum is actually depleted, which makes the fault easy to underestimate.

Common causes

  • Open signal wire or unplugged sensor connector
  • Open sensor ground/return circuit
  • Failed brake booster pressure sensor
  • Signal wire shorted to 5V or battery voltage
  • Corroded or backed-out connector terminals
  • Faulty PCM input circuit (rare)

Common misdiagnoses

  • Brake booster replaced for a wiring open
  • Vacuum pump replaced when it simply was never commanded on
  • Sensor replaced twice without finding the harness open
  • Master cylinder replaced for unrelated pedal complaints

Troubleshooting steps

  1. 1.Confirm the high signal on the scan tool

    A booster pressure sensor voltage PID pinned near 5V in all conditions confirms the high-input fault.

  2. 2.Inspect the sensor connector

    Verify the connector is fully seated and check for corroded, spread, or backed-out terminals at the sensor.

  3. 3.Check the ground/return circuit

    With key on and the connector back-probed, the sensor ground terminal should measure under 0.1V to battery negative; a high reading indicates an open return.

  4. 4.Jumper the signal to ground briefly

    With the sensor unplugged and key on, grounding the signal terminal through a fused jumper should drop the PID to 0V, proving the PCM and signal wire are good and isolating the sensor.

  5. 5.Test for a short to voltage

    If the signal stays high with the sensor unplugged and grounded-jumper testing fails, check the harness for a short to a 5V or 12V feed.

  6. 6.Verify after repair

    Apply vacuum with a hand pump and confirm the signal sweeps correctly, then clear the code and confirm no reset over a drive cycle.

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