Malfunction Indicator Lamp: Description and Operation

The MIL light is intended to alert the driver of certain malfunctions in the engine control system. If such a fault occurs, the EEC-IV processor will substitute a value or values and continue operating. In some cases this action may result in a slight change in vehicle driveability.
On 1988 models, the check engine light can be used to read codes. The check engine light on the front dash panel will remain on when a hard fault is present. During the Self-test sequence, a service code is reported by the check engine light. It will represent itself as a flash on the check engine light display on the dash panel. A single digit number of three will be reported by three flashes. However, as previously stated, a service code is represented by a two digit number, such as 2-3. As a result, the Self-test service code of 2-3 will appear on the check engine light display as two flashes, then after a two second pause, the light will flash three times.