Re: Brake Boost Sensor
alfa dealers have a list that is translated directly from italian, it can be very confusing.
in OBD books the sensor is called the "Brake Booster Pressure Sensor", but it is only really known as the vacuum assistance pressure sensor.
what does it do? the brakes are assisted by the vacuum created in the engine's intake, making it much easier to press your brake pedal. obviously this assistance is only requried when braking, so there is a pressure sensor on the master cylinder that controls when the vacuum assistance will be used.
p0555 means the fault is that there is no signal at all, which is often a circuit fault rather than a sensor fault, but it could be either.