While the engine is running, the malfunction indicator light (MIL) or Check Engine Light will light only if there is an emissions-related concern. The on-board diagnostic (OBD) generation two (II)system, which is standard on all 1995 and later model year vehicles, continuously monitors all engine and transmission sensors and actuators looking for electrical faults, as well as values that do not logically (rationally) fit with other powertrain data. When certain operating/driving conditions are met and a comprehensive monitor detects a failure that will result in emissions exceeding a pre-determined level, the computer stores a diagnostic trouble code, and illuminates the MIL. The OBD II system also actively tests some systems for proper operation while the vehicle is being driven. Fuel control and engine misfire are checked continuously, catalyst efficiency, exhaust gas recirculation operation, evaporative system integrity, oxygen sensor response, and the oxygen sensor heaters are tested once per trip when prerequisite operating conditions are met. The computer will illuminate the MIL if during these prerequisite operating conditions the system detects a failure that will cause a performance failure or result in emissions exceeding a predetermined level. Whenever an engine misfire severe enough to damage the catalytic converter is detected, the MIL will blink on and off rapidly. If this occurs, you should get off the road as quickly and safely as possible and shut the engine off. The vehicle should not be driven. Once lit, the MIL will remain on until the vehicle has been properly diagnosed and repaired. In the case of an intermittent/one-time failure, the light may turn off on its own once the diagnostic system has completed three consecutive "good trips" (three "trips" in which the fault is not detected). If the light has been on for more than a couple of days, you should have the system checked to prevent a potential breakdown. We have all the equipment necessary to reset the light and clear the diagnostic trouble code(s) from the system once repairs have been made.