Hard Failures
WARNING: This page is about a different car, the 1995 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.
Hard failures cause MIL to glow and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using self-diagnostic tests. If a sensor fails, PCM will use a substitute value in its calculations, allowing engine to operate in limp-in mode. In this condition, vehicle will run, but driveability may be poor.