Brake Booster Pressure Sensor Circuit Low
Code P0557 indicates the brake booster pressure sensor is detecting a voltage signal that is lower than the expected normal range. This sensor monitors vacuum pressure in the brake booster system, and a low signal suggests either a sensor malfunction, wiring issue, or loss of vacuum pressure in the booster.
What You Might Notice
- Check engine light (Service Engine Soon) illuminated
- Check brake light flashing or staying on during braking
- Increased brake pedal effort required to stop
- Soft or spongy brake pedal feel
- Reduced braking power or longer stopping distances
Most Common Causes
- 1
Defective Brake Booster Pressure Sensor
The pressure sensor itself may be faulty and sending an incorrect low voltage signal to the PCM even though brake booster pressure is normal.
- 2
Worn or Damaged Vacuum Lines
Cracks, leaks, or loose connections in vacuum hoses feeding the brake booster allow air to enter, reducing pressure and causing the sensor to read low.
- 3
Corroded or Damaged Connector
The pressure sensor connector may have corrosion or loose pins that prevent proper electrical communication between the sensor and PCM.
- 4
Faulty Brake Booster
The brake booster itself may have an internal leak or diaphragm failure, preventing normal vacuum pressure buildup that the sensor detects.
How to Diagnose It
- 1
Check Defective Brake Booster Pressure Sensor — The pressure sensor itself may be faulty and sending an incorrect low voltage signal to the PCM even though brake booster pressure is normal.
- 2
Check Worn or Damaged Vacuum Lines — Cracks, leaks, or loose connections in vacuum hoses feeding the brake booster allow air to enter, reducing pressure and causing the sensor to read low.
- 3
Check Corroded or Damaged Connector — The pressure sensor connector may have corrosion or loose pins that prevent proper electrical communication between the sensor and PCM.
- 4
Check Faulty Brake Booster — The brake booster itself may have an internal leak or diaphragm failure, preventing normal vacuum pressure buildup that the sensor detects.
How to Fix It
- 1
Replace Brake Booster Pressure Sensor
Locate the pressure sensor on or near the brake booster, disconnect the electrical connector, remove the old sensor, and install a new OEM or quality replacement sensor. Clear the code and test.
- 2
Inspect and Replace Vacuum Lines
Visually inspect all vacuum hoses connected to the brake booster for cracks, splits, or loose connections. Replace any damaged lines and ensure all connections are tight and seated properly.
- 3
Clean or Replace Sensor Connector
Disconnect the pressure sensor connector and inspect for corrosion or bent pins. Clean contacts with electrical contact cleaner, or if damage is severe, replace the connector or wiring harness.
- 4
Replace Brake Booster Assembly
If vacuum lines, sensor, and connector are all good but pressure signal remains low, the brake booster diaphragm may be ruptured. Remove the booster mounting bolts and replace the entire brake booster assembly.
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