Malfunction Indicator Lamp: Description and Operation

Malfunction Indicator Lamp

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.

Data Communications Link

Data Communications Link (DCL) Network:

The Data Communications Link (DCL) is a wiring system that allows the sharing of information between the Electronic Engine Control System (EEC-IV), the Electronic Instrument Cluster (EIC) and external equipment.

The EEC-IV system transmits the following information through the DCL to the EIC:
1. Engine RPM.
2. Engine coolant temperature.
3. EEC-IV malfunction indication.
4. Fuel used.

The DCL system transmits Malfunction Indicator Lamp (MIL) information to the EIC. The EIC uses MIL information to generate a CHECK ENGINE warning in the event of an engine sensor failure.

The EIC will display the message "CHECK DCL" on its Message Center Display if it is not receiving data from the EEC-IV. This warning is turned off whenever data communication is restored.

The EEC-IV monitors the Data Communication Link for faults. If a fault occurs in data communication a continuous Memory Code is set in the EEC-IV. The DCL Codes (529 for EEC-IV and 533 for EIC) can occur separately or together. These codes are not immediately cleared when data communication is restored.

The existance of a DCL code does NOT mean that a module has failed.