What Does P0555 Mean?
The ECM has detected a general malfunction in the brake booster pressure sensor circuit. This sensor measures vacuum or hydraulic pressure in the brake booster and provides the ECM with data for brake-assisted functions such as hill-start assist, brake-throttle override, and vacuum management. A circuit fault means the ECM cannot read the brake booster pressure reliably.
Safety Warning
Loss of brake booster pressure monitoring can disable safety features like hill-start assist and brake-throttle override. The driver may also not be alerted to brake booster vacuum loss, which could lead to a hard brake pedal requiring significantly more pedal effort to stop the vehicle.
Common Causes
35%
Failed brake booster pressure sensor with internal circuit failure producing no valid output signal
30%
Damaged or corroded wiring and connector at the brake booster pressure sensor due to moisture ingress in the engine bay
25%
Open or short circuit in the wiring between the brake booster pressure sensor and the ECM or brake control module
10%
ECM or brake control module internal fault on the brake booster pressure sensor input channel
Diagnostic Steps
1
Step 1: Locate the brake booster pressure sensor (typically mounted on or near the brake booster or master cylinder assembly). Inspect the sensor and connector for physical damage, moisture, and corrosion.
2
Step 2: With the key on engine off, verify 5V reference voltage and ground are present at the sensor connector. The signal wire should show a resting voltage between 0.5V and 1.5V with no vacuum applied.
3
Step 3: Start the engine (which creates intake manifold vacuum to the brake booster). The sensor voltage should rise to approximately 3.5-4.5V as vacuum builds. A fixed or absent reading indicates a sensor or circuit fault.
4
Step 4: If reference voltage is missing, check the 5V reference supply circuit for opens or shorts. This circuit is often shared with other sensors, so check if other sensor codes are present simultaneously.
5
Step 5: If wiring and voltage supply are confirmed good, replace the brake booster pressure sensor. Clear codes and verify the sensor reading changes appropriately when pumping the brake pedal with the engine off (depleting vacuum) and then starting the engine (restoring vacuum).
Estimated Repair Cost
$80 - $350
Parts + labor, varies by vehicle and location
The ECM has detected a general malfunction in the brake booster pressure sensor circuit. This sensor measures vacuum or hydraulic pressure in the brake booster and provides the ECM with data for brake-assisted functions such as hill-start assist, brake-throttle override, and vacuum management. A cir...
The most common cause of P0555 (Brake Booster Pressure Sensor Circuit) is: Failed brake booster pressure sensor with internal circuit failure producing no valid output signal
Typical repair costs for P0555 range from $80 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Loss of brake booster pressure monitoring can disable safety features like hill-start assist and brake-throttle override. The driver may also not be alerted to brake booster vacuum loss, which could lead to a hard brake pedal requiring significantly more pedal effort to stop the vehicle.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0555 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Brake Assist / Brake Booster System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
