Vacuum Reservoir Pressure Sensor Circuit Range/Performance

Possible causes

• CommonSplit, perished or disconnected vacuum hose
• CommonFailed non-return valve on the reservoir
• CommonFailed vacuum pump, on engines that use one
• CommonFailed pressure sensor
• PossibleCorroded connector or damaged wiring
• PossibleCracked or corroded reservoir

What you might notice

• Brake pedal harder than usual
• More pedal effort needed to stop
• Hissing from the pedal area
• Vacuum-operated actuators not working
• Check engine light on

What to check, in order

1. Test the brake pedal before driving. With the engine off, press it several times to use up the stored vacuum, then start the engine with your foot on the pedal - it should sink slightly as assistance arrives. If it does not, assistance is genuinely missing.
2. Check the vacuum hoses and the non-return valve for splits, looseness and perishing.
3. On a diesel or a direct-injection petrol engine, check the vacuum pump - these engines make little vacuum of their own and depend on it.
4. Inspect the sensor connector for corrosion.
5. Check the reference voltage and earth at the sensor.