For 1990-2009 cars

### Circuit Description

The Diagnostic System Check - Automatic Transmission is an organized approach to identify a condition created by an automatic transmission. The Diagnostic System check is the diagnostic starting point for an automatic transmission concern. 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 concern 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 DTC will erase all Freeze Frame/Failure Records stored in engine control module (ECM) memory.

• | Poor engine performance can sometimes be mis-diagnosed as a transmission concern. In order to avoid unnecessary transmission work, always perform the Diagnostic System Check - Vehicle .

• | 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:

- | ECM 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. This step determines if the transmission control module (TCM) is transmitting serial data to the DLC and that the serial data circuit is not open or shorted.

3. This step determines if an TCM DTC is current or stored in history.

4. This step determines if the ECM is transmitting serial data to the DLC and that the serial data circuit is not open or shorted.

5. This step determines if an ECM DTC is current or stored in history.

Step | Action | Yes | No
--- | --- | --- | ---
1 |

1. Install a scan tool.

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 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 power up?

Go to Step 2

Go to Scan Tool Does Not Power Up

2 | Attempt to establish communication with the transmission control module (TCM). Does the scan tool communicate with the TCM? | Go to Step 3 | Go to Scan Tool Does Not Communicate with CAN Device
3 | Select the TCM DTCs function on the scan tool. Does the scan tool display any TCM DTCs? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 4
4 | Attempt to establish communication with the engine control module (ECM). Does the scan tool communicate with the ECM? | Go to Step 5 | Go to Scan Tool Does Not Communicate with CAN Device
5 | Select the ECM DTCs function on the scan tool. Does the scan tool display any ECM DTCs? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Symptoms - Automatic Transmission