For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

### Circuit Description

The Service Transmission Lamp (STL) should illuminate briefly when the ignition switch is turned on. Then the STL should go out. The 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 for Intermittents.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. 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.

2. If the other indicator lamps in the instrument cluster are functioning, the feed circuit is OK.

3. 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.

4. If the STL is on with the TCM connected and off with the TCM disconnected and no DTCs are set, there is a problem in the TCM.

5. 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.

#### Service Transmission Lamp (STL) Diagnosis

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Transmission On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to On-Board Diagnostic System Check
2 | Turn on the ignition with the engine off. Does the STL illuminate for approximately 3 seconds? | -- | Go to Step 6 | Go to Step 3
3 | Check the fuse for the instrument cluster ignition feed circuit. Is the fuse OK? | -- | Go to Step 4 | Go to Step 9
4 |

1. Turn off the ignition.
2. Disconnect the TCM.
3. Turn on the ignition.
4. With a fused jumper, jumper the STL control circuit in the TCM harness connector to ground.

Is the STL on?

--

Go to Step 10

Go to Step 5

5 | Check the STL circuit for the following conditions:

• | Damaged bulb (refer to Engine Electrical ).

• | Open ignition feed to the bulb (refer to Engine Electrical ).

• | Control circuit open or shorted to B+.

Is the action complete?

--

Go to Step 12

--

6 | Use the scan tool in order to verify that no DTCs are set. Are there any DTCs displayed? | -- | Go to the applicable DTC table | Go to Step 7
7 |

1. Turn off the ignition.
2. Disconnect the TCM.
3. Turn on the ignition with the engine off.

Does the STL illuminate?

--

Go to Step 8

Go to Step 11

8 | Repair the short to ground in the STL control circuit. Is the action complete? | -- | Go to Step 12 | --
9 | Repair the short to ground in the feed circuit to the instrument panel indicator lamps. Is the action complete? | -- | Go to Step 12 | --
10 | Check the TCM harness connector for a poor connection or poor terminal tension. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. Was a problem found and corrected? | -- | Go to Step 12 | Go to Step 11
11 | Replace the TCM. Refer to TCM Replacement . Is the action complete? | -- | Go to Step 12 | --
12 | Start the engine and observe the STL. Does the STL turn on briefly and then turn off? | -- | System OK | Refer to the Test Description