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DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P0558

P0558Brake Booster Pressure Sensor Circuit High Input

P0558 means the powertrain control module (PCM) is seeing a voltage signal from the brake booster pressure sensor that is higher than the expected range for the current operating conditions. The sensor normally produces a voltage that varies with the vacuum or pressure inside the brake booster, and an abnormally high reading tells the PCM that the circuit is likely open, shorted to voltage, or the sensor has failed.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • Illumination of the check engine light or service engine soon light, often with no other noticeable symptoms
  • A hard brake pedal that requires noticeably more effort to stop the vehicle
  • Reduced power brake assist, especially at low engine speeds or during repeated brake applications
  • An intermittent or constant warning message related to the brake system on vehicles with driver information displays
  • Possible rough idle or engine stalling if the fault affects the vacuum supply to the booster
  • Cruise control or other driver-assist features may become unavailable because they rely on brake pressure data

Common causes, most likely first

  1. Open or high-resistance wiring in the sensor signal circuit, including a broken wire or poor connector terminal
  2. Short to voltage on the sensor signal circuit, often from chafed insulation against a nearby power wire
  3. Failed brake booster pressure sensor that is internally shorted or has drifted out of calibration
  4. Loose, corroded, or water-intruded electrical connector at the sensor or at the PCM
  5. Faulty PCM driver or internal reference voltage circuit, though this is less common than wiring or sensor faults
  6. Blocked or disconnected vacuum hose between the engine and brake booster causing the sensor to read an implausible pressure
  7. Aftermarket or incorrect sensor installed previously that does not match the vehicle's calibration

How to diagnose and fix it

  1. Connect a scan tool and record the freeze-frame data and live brake booster pressure sensor voltage to confirm the high reading matches the code
  2. Visually inspect the sensor, its connector, and the wiring harness for damage, corrosion, or loose terminals, and repair as needed
  3. Check the sensor's reference voltage and ground circuits with a digital multimeter to rule out a supply-side problem before condemning the sensor
  4. Perform a voltage drop test on the signal circuit while wiggling the harness to catch intermittent opens or shorts
  5. Compare the sensor reading with a known-good vacuum gauge or scan tool data from a similar vehicle to verify the sensor's accuracy
  6. Replace the brake booster pressure sensor if the circuit tests good but the high voltage reading persists, then clear the code and verify the repair
  7. If the code returns after sensor replacement, diagnose the PCM and its internal driver circuit before replacing any more parts

What a high booster sensor reading really tells you

  • A high voltage on the signal circuit often means the circuit is open rather than the sensor being bad, so a broken wire or unplugged connector is a common culprit that gets missed when the sensor is replaced first.
  • Some vehicles use the brake booster pressure sensor for more than brake assist; it also feeds data to the stability control and cruise control systems, so a fault can disable those features without any brake pedal symptom.
  • A vacuum leak at the booster check valve or a collapsed vacuum hose can make the sensor read outside its expected range and set P0558 even though the sensor and wiring are perfectly fine.
  • The code can set intermittently from water intrusion into the connector after a car wash or heavy rain, so a thorough inspection of the connector seals is worth doing before any parts are ordered.
  • Technicians sometimes overlook a poor ground for the sensor circuit, which can cause a high signal voltage reading that mimics a short to voltage and leads to unnecessary PCM replacement.

Can I keep driving with P0558?

You can usually drive the vehicle to a repair shop, but be aware that power brake assist may be reduced, so allow extra stopping distance and avoid heavy brake applications. If the pedal feels hard or braking effort increases noticeably, stop driving and have the vehicle towed to prevent a safety risk.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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