Engine Controls - Theory & Operation: Self-Diagnostics: Notes

The ECM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, ECM will illuminate the "SERVICE ENGINE SOON" light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in ECM memory. Malfunctions are designated as either "hard failures" or as "intermittent failures". To retrieve stored codes, see the appropriate G - TEST W/ CODES article in this section.