Service Transmission Lamp Diagnosis Early Production
Circuit Description
The service transmission lamp (STL) should illuminate briefly when the ignition switch is on and then go out. Ignition voltage is supplied directly to the indicator bulb. The transmission control module (TCM) controls the lamp by grounding the control circuit via an internal solid state device called a driver.
Diagnostic Aids
An intermittent may be caused by the following:
| • | Corrosion |
| • | Mis-routed harness |
| • | Rubbed through wire insulation |
| • | Broken wire inside the insulation |
Refer to Symptoms in Engine Controls for Intermittents.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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This step determines whether you were sent here because of an inoperative STL, or because of a STL that is always on with no DTCs set.
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If the other indicator lamps in the instrument cluster are functioning, the feed circuit is OK.
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This step verifies that the STL is on with no DTCs set. If a DTC is displayed, return to the Transmission On-Board Diagnostic (OBD) System Check.
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If the STL is on with the TCM connected and off with the TCM disconnected and no DTCs are set, there is a condition in the TCM.
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After the engine starts, the STL should illuminate briefly and then go out. If the STL remains on, go back to the Transmission OBD System Check.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the On-Board Diagnostic System Check performed? | -- | ||||||||
Turn the ignition switch to the RUN position. Does the STL illuminate? | -- | |||||||||
3 | Check the fuse for the instrument cluster ignition feed circuit. Is the fuse OK? | -- | ||||||||
4 |
Is the STL on? | -- | ||||||||
Check the STL circuit for the following conditions:
Refer to General Electrical Diagnosis in Wiring Systems. Is the action complete? | -- | -- | ||||||||
Use the Scan Tool in order to verify that no DTCs are set. Are there any DTCs displayed? | -- | |||||||||
Does the STL illuminate? | -- | |||||||||
8 | Repair the short to ground in the STL control circuit. Is the action complete? | -- | -- | |||||||
9 | Repair the short to ground in the feed circuit to the instrument panel indicator lamps. Is the action complete? | -- | -- | |||||||
10 | Check the TCM harness connector for a poor connection or poor terminal tension. Refer to General Electrical Diagnosis in Wiring Systems. Was a condition found and corrected? | -- | ||||||||
11 | Replace the TCM. Refer to Transmission Control Module Replacement . Is the action complete? | -- | -- | |||||||
Start the engine and observe the STL. Does the STL illuminate briefly and then go out? | -- | System OK
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