For 1990-2009 cars

### Circuit Description

The data link connector (DLC) provides operating power for the scan tool at terminal 16 (battery positive voltage) and at terminal 4 (ground). The DLC provides the class 2 serial data signals at terminal 7. The scan tool will power up with the ignition OFF. Many modules, however, will not communicate unless the DIM detects that the ignition is ON and sends the appropriate power mode message.

### Test Description

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

1. The OBD fuse supplies power to terminal 16 of the DLC.

2. The battery positive voltage and ground circuits of the DLC are functioning properly. The malfunction must be due to the scan tool.

Step | Action | Yes | No
--- | --- | --- | ---
1 | Test the battery positive voltage circuit of the DLC for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | System OK | Go to Step 2
2 | Test the ground circuit at terminal 4 of the DLC for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to the applicable Diagnostic System Check | Go to Step 3
3 | Inspect for poor connections at terminals 4 and 16 of the DLC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to the applicable Diagnostic System Check | Go to Step 4
4 | The scan tool may be malfunctioning. Refer to the scan tool user guide. Did you obtain a properly operating scan tool? | Go to the applicable Diagnostic System Check | --