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C0556 Chassis

Brake Booster Pressure Sensor Performance

The brake booster vacuum or pressure sensor signal does not respond plausibly to engine vacuum or electric booster activity.

Affected components

  • Brake booster vacuum sensor
  • Vacuum pump

Common causes

  • High likelihood: Vacuum leak in booster line
  • Medium likelihood: Vacuum pump weak
  • Low likelihood: Sensor element aged beyond calibration window

Possible symptoms

  • ABS warning light on
  • ESC/stability control deactivated
  • Possible reduced brake assist
  • Speedometer may behave erratically

Sources

Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.

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