Malfunction Indicator Lamp: Service and Repair

The check engine lamp will be illuminated when the ignition switch is placed in the On position. When the engine is started, the lamp should go off. If the lamp remains On for 10 seconds or constantly after the engine is started, the self diagnosis system has detected a problem and has stored a code in the system Electronic Control Module (ECM). After diagnosis and repair, the ECM memory can be cleared of codes as follows:

On models except Cadillac with DEFI and 1986-88 Buick Reatta/Riviera and Oldsmobile Toronado/Trofeo, remove the ECM fuse or disconnect the battery ground cable for approximately 30 seconds, with ignition switch in the Off position. It should be noted, if battery ground cable is disconnected to clear codes, components such as clocks, electronically tuned radios etc., will have to be reset.

On vehicle that are equipped as such, the ECM power feed is connected by a pigtail, inline fuse holder, at the positive battery terminal. To clear codes within the ECM system and protect the components that need resetting, disconnect the inline fuse.

On 1980-85 Cadillac models with DEFI engines, depress Electronic Climate Control Off and Hi buttons to clear codes. On 1986-92 Cadillac DeVille and Fleetwood models, depress Off and Lo button on the Electronic Climate Control to clear stored BCM codes. Depress Off and Hi to clear stored ECM codes.

On Cadillac Eldorado and Seville and 1986-88 Buick Reatta/Riviera and Oldsmobile Toronado/Trofeo models, the stored codes are cleared during the self-diagnostic procedure.