Sensor performance monitoring

A method is described for monitoring the performance of a sensor used to measure a vehicle or engine operating parameter in an automotive vehicle having an internal combustion engine (10) with an intake manifold (44) coupled through a check valve (34) to a brake booster (130). The method comprises measuring a brake booster pressure (P66), calculating an estimate of the operating parameter based on the brake booster pressure, and determining degradation of the sensor (142) based on a comparison of the measurement of the operating parameter derived from the sensor with the estimate calculated on the basis of the brake booster pressure.