Schematic Reference: Engine Controls Schematics
Circuit Description
There should always be a steady malfunction indicator lamp (MIL) when the ignition switch is in the ON position and the engine is not running. System voltage is applied to the indicator lamp when the ignition is ON and when the engine is running. The engine control module (ECM) controls the MIL and illuminates the lamp by providing a ground path through the MIL control circuit.
Diagnostic Aids
Check for any of the following conditions:
| • | If the engine runs OK, check for a faulty indicator bulb, or an open in the instrument cluster power circuit. |
| • | With no MIL and the engine cranks but will not start, check for a faulty Main Relay. |
| • | With no scan tool data, no MIL, and the engine cranks but will not start, check for a shorted to ground 5 volt reference circuit (i.e. TP sensor, MAP sensor, fuel tank pressure sensor). |
| • | If the engine cranks but will not run, check for an open in the ECM ignition circuit or the battery feed circuit or for a faulty ECM to engine ground circuit. |
An intermittent malfunction may be caused by a fault in an MIL control system electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connector locks. |
| • | Improperly formed or damaged terminals. |
| • | Faulty terminal to wire connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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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.
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Checks the ground circuits to the ECM.
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This step will verify whether the MIL circuit is at fault or if the ECM is not providing a ground path for the MIL circuit.
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This step check whether ignition battery positive is being provided to the MIL circuit.
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This step will verify the condition of the MIL control circuit. The ECM is providing the ground for the test light.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||
2 | Check for an open in the IG-COIL METER fuse. Was the IG-COIL METER fuse open? | -- | ||||||||
3 | Attempt to start the engine. Does the engine start? | -- | ||||||||
Does the test light illuminate at each terminal? | -- | |||||||||
5 | Repair the open in the ECM ground circuit(s) between the ECM and the G103 ground. Is the action complete? | -- | -- | |||||||
Does the MIL illuminate? | -- | |||||||||
Did test light illuminate? | -- | |||||||||
Does the test light illuminate when the ignition switch is turned ON, and does the test light go OFF when the ignition switch is turned OFF? | -- | |||||||||
9 | Repair the open in the BLK/WHT wire between the Junction Block and the I/P cluster assembly. Is the action complete? | -- | -- | |||||||
10 | Locate and repair the open in the PPL/YEL wire between the I/P cluster assembly and the ECM. Is the action complete? | -- | -- | |||||||
11 |
Is the action complete? | -- | -- | |||||||
12 | Repair the short to ground in the IG-COIL METER fuse circuit. Is the action complete? | -- | -- | |||||||
13 | Replace the ECM. Refer to Engine Control Module Replacement. Is the action complete? | -- | -- | |||||||
14 | After repairs start the vehicle and observe the MIL. Did the MIL illuminate for approximately 3 seconds and then turn OFF? | -- | System OK | Go to the Applicable Table |
