P0557: Brake Booster Pressure Sensor Circuit Low Input
What to do
Check that the brake pedal feels normal with the engine running. If it does, this is likely to be an electrical fault rather than a braking one.
What this code means
The brake booster pressure signal is below its plausible range. Whether that corresponds to plenty of vacuum or none depends on the sensor's polarity, which varies by manufacturer — so the reading direction alone does not tell you whether the brakes are assisted. Confirm at the pedal rather than inferring from the code.
Likely causes
Start here
- Signal wire shorted to ground · moderate
- Faulty brake booster pressure sensor · moderate
- Corroded or loose connector · easy
Less common
- Failed sensor reference voltage supply · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
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