Circuit Description
Ignition 1 voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.
MIL Operation
The MIL is located on the instrument panel (I/P).
MIL Function
| • | The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible. |
| • | The MIL illuminates during a bulb test and a system test. |
| • | A DTC will be stored if a MIL is requested by a diagnostic. |
MIL Illumination
| • | The MIL will illuminate with ignition switch ON and the engine not running. |
| • | The MIL will turn OFF when the engine is started. |
| • | The MIL will remain ON if the self-diagnostic system has detected a malfunction. |
| • | The MIL may turn OFF if the malfunction is not present. |
| • | If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON. |
| • | If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON. |
Diagnostic Aids
An open ignition fuse F4 will cause the entire cluster to be inoperative.
Inspect the battery and ignition feed circuits for poor connections if the MIL is intermittent.
Any circuitry that is suspected as causing an intermittent complaint should be thoroughly inspected for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to the wiring harness.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the condition is with the MIL control circuit or the ECM.
-
This step determines if a voltage is constantly being applied to the control circuit.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connect End View Reference: Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Step 2 | |
2 |
Are other indicator lamps inoperative? | Go to Symptoms - Instrument Panel, Gages and Console in Instrument Panel, Gages, and Console | Go to Step 3 |
3 |
Does the MIL turn ON and OFF when commanded with a scan tool? | Go to Intermittent Conditions | Go to Step 4 |
Is the MIL illuminated? | Go to Step 8 | Go to Step 5 | |
Did the fuse in the jumper wire open? | Go to Step 9 | Go to Step 6 | |
6 |
Did you find and correct the condition? | Go to Step 13 | Go to Step 7 |
7 | Test for an intermittent and for a poor connection at the I/P. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 10 |
8 | Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
9 | Repair the short to voltage in the MIL control circuit. Did you complete the repair? | Go to Step 13 | -- |
10 | Inspect the MIL for an open. If the lamp is open, replace the lamp. Refer to Instrument Cluster Bulb Replacement in Instrument Panel, Gages, and Console. Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
11 | Replace the instrument panel cluster. Refer to Instrument Panel Assembly Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement? | Go to Step 13 | -- |
12 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | Go to Step 13 | -- |
13 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
