Abstract: An on-board diagnostic system of a vehicle comprises disabling diagnostic operation, such as a misfire monitor, based on road roughness. In one example, the disabling of the diagnostic operation is based on brake actuation and degradation of an anti-lock braking system.

Abstract: An on-board diagnostic system of a vehicle comprises a diagnostic component configured to detect a vehicle operating condition and to produce an error output when the vehicle operating condition is determined to be abnormal; and a rough road detector configured to determine an average level of roughness of a road surface based on signals from wheel speed sensors, to compare the roughness with a predetermined threshold, and to disable the error output of the diagnostic component or switch to an alternate calibration for the diagnostic component if the roughness level has exceeded the predetermined threshold.

Abstract: A method is provided for controlling an engine in a vehicle to facilitate determination of engine position sensor correction factors. The vehicle includes a motor, which is operatively connected to the engine, a sensor configured to detect engine position, and a controller, which is in communication with the engine, the sensor and the motor. It is determined when an engine shutdown is requested, for example, when the controller commands the vehicle to be powered by the motor. It is next determined whether engine position sensor correction factors are known. If they are, the engine control routine is stopped. If the correction factors are not known, fuel to the engine is discontinued, and the motor is employed to spin the engine at an approximately constant speed. The engine position sensor correction factors can then be determined while the engine is rotating in a defueled state.