Refer to
Ignition, Ground, and MIL Voltage
.
Circuit Description
When the ignition is turned ON, the MIL will momentarily flash ON then OFF then remain ON until the engine is running, if no diagnostic trouble codes (DTCs) are stored. Battery voltage is supplied through the ignition switch directly to the malfunction indicator lamp (MIL) telltale. The powertrain control module (PCM) controls the MIL by providing a ground path through the MIL control circuit in order to turn ON the MIL.
Diagnostic Aids
An open ignition fuse causes the MIL to be inoperative.
Check any circuitry that is suspected of causing an intermittent problem for the following conditions:
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Physical damage to the wiring harness |
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 and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
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If the engine fails to start and the MIL is inoperative then the fault can be isolated to either the PCM ignition feed, the battery feed, a poor PCM ground at the engine block, or the PCM.
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A MIL that responds correctly to the scan tool command indicates that the fault is not present or that the condition caused the No MIL condition has been corrected.
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Probing the MIL circuit with a test lamp to ground simulates the PCM's control of the MIL.
-
Locate and repair any shorts that may have caused the fuse to open before replacing the fuse.
-
Reprogram the replacement PCM. Refer to the latest Techline information for programming procedures.
Before replacing the PCM, check the terminals for the following conditions:
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For MIL bulb replacement procedures, refer to MIL Bulb Repair in Section 8C of the service manual.
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The PCM grounds will only cause a problem if all the grounds are not making a good connection. Whenever a PCM ground problem is suspected, the most probable place to check is where all the grounds meet at the engine block.
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wiring connections or physical damage to the wiring harness. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
2 | Turn the ignition ON leaving the engine OFF. Is the MIL ON? | -- | ||
Attempt to start the engine. Does the engine start? | -- | |||
Does the MIL turn ON and OFF when commanded? | -- | |||
Is the MIL ON? | -- | |||
Inspect the ignition fuse and the battery feed fuse. Are the fuses OK? | -- | |||
7 | With a test lamp connected to a ground, probe the ignition feed terminal #2. Does the test lamp illuminate? | -- | ||
8 | Did the test lamp illuminate? | -- | ||
9 |
Does the test lamp illuminate? | -- | ||
10 |
Is the action complete? | -- | -- | |
Is the action complete? | -- | -- | ||
12 | Repair the open ignition feed circuit #2. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
13 | Repair the short to voltage in the MIL control circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
14 |
Was a repair necessary? | -- | ||
15 |
Was a repair necessary? | -- | ||
Was a bulb replacement necessary? | -- | |||
17 | Replace the Instrument Panel Cluster. Refer to Engine Electrical. Is the action complete? | -- | -- | |
18 | Probe the battery feed #1 circuit with a test lamp connected to a ground. Does the test lamp illuminate? | -- | ||
19 | Repair the open ignition feed #1 circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
Is the action complete? | -- | |||
21 | Repair the open battery feed circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
22 |
Does the engine start and continue to run. | -- | ||
23 |
Are any DTCs displayed? | -- | Go to the Applicable DTC Table | System OK |
