Refer to
Power and Ground
and to
MIL and DLC
.
Circuit Description
The malfunction indicator lamp (MIL) is illuminated when the ignition is on and the engine is off. Battery ignition voltage is supplied to the MIL. The powertrain control module (PCM) will turn the MIL on by grounding the lamp control circuit. The MIL is normally off when the engine is running.
Diagnostic Aids
Check for any of the following conditions:
| • | Check for a faulty indicator bulb, or an open in the instrument cluster power circuit if the engine starts and runs OK. |
| • | Check for a faulty main relay if there is no MIL and the engine cranks but will not start. Refer to Main Relay Circuit Diagnosis . |
| • | A MIL that is dim or not illuminated steady can be caused by an inadequate PCM ground. Inspect G102 for a clean, tight connection. |
| • | A faulty electrical connection to the PCM. |
An intermittent malfunction may be caused by a fault in the MIL electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Any backed-out terminals |
| • | Any improper mating of terminals |
| • | Any broken electrical connector locks |
| • | Any improperly formed or damaged terminals |
| • | Any faulty terminal-to-wire connections |
| • | Any physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Any corrosion of the electrical connections, the splices, or the terminals |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
If the engine does not start, the PCM is probably not turning on the MIL. A PCM that does not have adequate ignition power or good electrical ground circuits, may not operate the MIL or start the engine.
-
This step will verify whether the MIL circuit is at fault or if the PCM is not providing a ground path for the MIL circuit.
-
This step will verify the condition of the MIL control circuit. The PCM is providing the ground for the test lamp.
-
This step checks for an open in the ignition positive voltage circuit that supplies the PCM. An open in this circuit will disable the PCM and the main relay. The engine will not start or run, and there will be no MIL control or serial data if the circuit is open.
-
This step tests for whether the PCM is turning ON the main relay. The MIL will not illuminate if the main relay is malfunctioning.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||
2 | Check for an open in the following fuses:
Was an open fuse found? | -- | ||||||||
Attempt to start the engine. Does the engine start and run? | -- | |||||||||
Does the MIL illuminate? | -- | |||||||||
5 |
Does the test lamp illuminate? | -- | ||||||||
Does the test lamp illuminate when the ignition switch is turned ON, and go off when the ignition switch is turned OFF? | -- | |||||||||
7 | Repair the open in the BLK/WHT wire between the junction block and the instrument cluster. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
8 | Locate and repair the open in the PPL/YEL wire between the instrument cluster and the PCM. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
Does the test lamp illuminate? | -- | |||||||||
10 | Repair the open in the ignition positive voltage circuit between the IG fuse and the PCM. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
11 |
Does the test lamp illuminate at each terminal? | -- | ||||||||
Does the test lamp illuminate? | -- | |||||||||
13 | Repair the open in the PCM ground circuits between the PCM and the G102. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
14 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |||||||
15 |
Is the action complete? | -- | -- | |||||||
16 | Repair the short to ground in the IG fuse or the FI fuse circuits. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
17 |
Does the MIL illuminate when the ignition is on and turn OFF after the engine was started? | -- | System OK |
