Service Engine Soon Light

On carbureted models, a SERVICE ENGINE SOON light driver module is installed in wiring harness from ECM to SERVICE ENGINE SOON light. This driver turns on light when ignition is turned on. When vehicle starts, ECM turns light off. If ECM malfunctions or senses a malfunction, light will turn back on. On fuel injected models, driver is an integral part of ECM and is not serviceable.

As a bulb and system check, SERVICE ENGINE SOON light will glow when ignition switch is turned to ON position and engine is not running. When engine is started, light should go out. If not, a malfunction has been detected in the computerized engine control system or SERVICE ENGINE SOON light circuit is faulty. Light may be used on some models to display stored trouble codes. To access codes using Scan or Non-Scan methods, see appropriate TESTS W/CODES article in this section. See the table below.