Hard Failures
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 1990 Pontiac Grand Am, 1990 Pontiac 6000, 1990 Oldsmobile Cutlass Cruiser, 1990 Oldsmobile Cutlass Ciera, and 1990 Oldsmobile Cutlass Calais. However, it is still accessible from the selected car via links, so may be relevant.
Hard failures cause SERVICE ENGINE SOON light to illuminate 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 diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely be encountered.