GM Service Manual Online
For 1990-2009 cars only

The Diagnostic System Check - Automatic Transmission is an organized approach to identifying a condition created by an electronic transmission control system. The Diagnostic System Check - Automatic Transmission is intended for use in diagnosing a vehicle with separate engine and transmission control modules, ECM and TCM.

Diagnostic Aids

Inspect all of the related wiring and connections including the connections at the TCM, as these may cause an intermittent concern. Inspect the terminals for any damage or any corrosion. Inspect the connector for any pushed-out terminals.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

Do not perform the Diagnostic System Check - Automatic Transmission unless one of the concerns listed is present. Failure to follow this procedure could lead to misdiagnosis of the system.

Step

Action

Yes

No

1

Note the A/T warning lamp as the ignition switch is turned to ON.

Does the A/T warning lamp illuminate steady for 3 seconds and then go OFF?

System OK

Go to Step 2

2

Does the A/T warning lamp flash continuously?

Go to Automatic Transmission Warning Lamp Flashes Continuously

Go to Step 3

3

Display flash code DTCs. Refer to Reading Diagnostic Trouble Codes .

Are there any DTCs displayed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 4

4

  1. Turn the ignition switch to the OFF position.
  2. Intermittent DTCs are indicated. Refer to Diagnostics Aids for that specific DTC.

Are all DTCs diagnosed and malfunctions repaired?

Go to Symptoms - Automatic Transmission

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