OBD-II Code P0558 — What It Means & How to Fix It

What Does This Error Mean?

P0558 means the brake booster pressure sensor circuit is reading a voltage that is higher than the expected maximum. A high signal typically points to an open circuit — a broken wire, disconnected connector, or a sensor that has failed with its signal pulled high. This is a brake system code and should be addressed promptly. Check your brake pedal feel — if stopping requires more effort than usual, seek service immediately.

Affected Models

2005 and newer vehicles with electronic brake booster pressure monitoring
All Toyota hybrid vehicles — Prius, Highlander Hybrid, Camry Hybrid
Ford F-150, Expedition, and Explorer models with vacuum booster sensors
Chevrolet Silverado and Tahoe models with monitored brake boost systems
European vehicles with active brake boost monitoring — BMW, Audi, Volkswagen, Mercedes-Benz

Common Causes

Open circuit in the sensor signal wire — broken wire or disconnected harness between the sensor and PCM
Brake booster pressure sensor has failed with the signal wire pulled high (open failure mode)
Sensor connector has fully disconnected or has a terminal that has backed out of the connector
Short to voltage on the signal wire — the signal wire has contacted a live power wire in the harness
PCM input circuit fault causing the sensor reading to be interpreted as above maximum range

How to Fix It

Before anything else — check your brake pedal feel with the engine running. Press the pedal normally and assess whether it feels harder than usual or whether stopping distance seems longer. If braking is impaired, do not drive the vehicle further.

Even with P0558 active, the physical brake booster may still be functioning if the fault is in the sensor circuit only. But you must confirm this before driving.
Locate the brake booster pressure sensor — it is typically on the booster body on the driver's side firewall. Check the connector first. An unplugged or partially connected sensor will cause a high circuit reading because the PCM input is left floating high.

Push the connector in firmly until it clicks. Clear the code and test drive — if it does not return, the connector was the entire problem.
Inspect the wiring harness between the sensor and the PCM for any broken, cut, or disconnected wires. A broken signal wire leaves the PCM input floating high, which triggers P0558. Look for pinch points, sharp edges, and anywhere the harness is under tension.

Check the harness routing at the firewall pass-through — wiring commonly chafes and breaks at grommets.
With the connector plugged in and the ignition on, use a scan tool to check the brake booster pressure sensor live reading. The value should be in a reasonable range — not at maximum scale. If the reading is pegged at the maximum value, the circuit is open.

Cross-reference the reading with the brake pedal test result. A sensor reading maximum pressure while the pedal feels soft is contradictory and confirms a sensor or circuit fault.
Replace the brake booster pressure sensor if wiring checks out. On most vehicles the sensor threads directly into the booster. Remove the connector, unscrew the sensor with the correct socket, install the replacement, reconnect, and clear the code. Verify correct operation with a scan tool.

Confirm the replacement sensor reads plausible values during a test drive — it should change predictably when the brake pedal is pressed.

When to Call a Professional

This is a brake system fault and braking safety may be compromised. Do not delay diagnosis if your pedal feel has changed. A shop can quickly test the sensor circuit and confirm whether the sensor, wiring, or booster itself is at fault. Typical repair cost ranges from $150 for a sensor to $500 or more for a failed booster.

Frequently Asked Questions

Why does an open circuit cause a high reading rather than a low reading?

In most automotive sensor circuits, the PCM applies a 5-volt reference voltage to the signal wire through a pull-up resistor inside the PCM. When the sensor is connected, it pulls the voltage down to a level proportional to the measured value. When the circuit is open (broken wire or disconnected sensor), nothing pulls the voltage down and it stays at or near 5 volts — which the PCM interprets as a high reading.

Can P0558 come and go intermittently?

Yes — intermittent P0558 is usually caused by a loose connector or a wire that is almost but not quite broken. Vibration or movement causes the connection to open and close. To find an intermittent fault, wiggle the harness and connector while monitoring sensor voltage with a scan tool.

Will replacing the sensor fix P0558 if the wiring is broken?

No — if the harness has a broken wire, replacing the sensor will not fix the code. Always test the wiring first. Replacing parts without testing is expensive and the code will return.