GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Chevy C Cab/Chassis HD (GMT 400) 🢒 Engine 🢒 Engine Electrical 🢒 Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission

Circuit Description

The Automatic Transmission Diagnostic System Check is an organized approach to identify a problem created by an automatic transmission. The Diagnostic System check is the diagnostic starting point for an automatic transmission complaint. The Diagnostic System Check directs you to the next logical step for diagnosing a transmission concern. Perform this check only if there is a driveability complaint or if you have been directed here from another service information section.

Follow the table to help reduce diagnostic time and help prevent unnecessary replacement of good parts.

Diagnostic Aids

Important: 

   • Do not clear the DTC unless directed by a diagnostic procedure. Clearing the DTCs will erase all Freeze Frame and Failure Records stored in PCM memory.
   • Poor engine performance can sometimes be diagnosed as a transmission driveability condition. In order to avoid mis-diagnosis of the automatic transmission, always perform Diagnostic System Check - Engine Controls in Engine Controls - 6.5L or Diagnostic System Check - Engine Controls in Engine Controls - 8.1L.

    • Use a scan tool that is known to function correctly. If necessary, test the scan tool on another vehicle.
    • Ensure the scan tool contains the most current file available.
    • The scan tool will display a loss of communication error message under the following conditions:
       - PCM power is interrupted
       - The ignition switch is turned OFF
       - The battery voltage level is very low
       - A poor connection at the diagnostic link connector (DLC)

Test Description

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

  1. This step determines if the scan tool is receiving power through the DLC connector.

    2.

  2. The MIL should illuminate whenever the ignition is ON and the engine is not running.

    3.

  3. This step determines if the PCM is transmitting Class 2 serial data to the DLC and that the Class 2 data circuit is not open or shorted.

    4.

  4. This step determines if a DTC is current or stored in history.

Step

Action

Yes

No

1

  1. Install a scan tool.

    2. Important: 

       • Check for applicable service bulletins before proceeding with this test. Perform this test only if there is a driveability complaint or if you have been directed to this table from another section in the service information.
       • Do not turn the ignition OFF when performing this diagnostic procedure. Do not clear the DTCs unless instructed by this diagnostic procedure.

  2. Turn ON the ignition, with the engine OFF.

Does the scan tool turn ON?

Go to Step 2

Go to Scan Tool Does Not Power Up in Data Link Communications

2

Is the MIL ON?

Go to Step 3

Go to Malfunction Indicator Lamp Circuit Check in Engine Controls - 6.5L or DTC P0650 in Engine Controls - 8.1L

3

Attempt to establish communication with the PCM controller module or modules.

Does the scan tool communicate with the PCM control module or modules?

Go to Step 4

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

4

Important: Diagnostic Trouble Codes (DTCs), engine performance, and transmission default actions can greatly affect the transmission performance. Ensure that these items are not the cause of a transmission concern.

Use the scan tool Capture Info function in order to save or capture, Store Info, any DTC Information.

Are there any DTCs present?

Go to Diagnostic Trouble Code (DTC) List/Type

Go to Symptoms - Automatic Transmission