For 1990-2009 cars

### Circuit Description

The data link connector (DLC) provides operating power for the scan tool at terminal 16. The ground for the scan tool is provided at terminal 4. The 16 pin DLC provides the serial data signals at terminal 7 ECM, TCM, terminal 3 speed sensitive power steering, terminal 12 EBCM, and terminal 13 SIR serial data. The scan tool will power up with the ignition OFF. The ignition must be ON in order for the scan tool to communicate with a control module.

### Test Description

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

1. Fuse F16 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
--- | --- | --- | ---
Schematic Reference: Data Communication Schematics
1 | Test the battery positive voltage circuit of the data link connector (DLC) for an open or short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 5 | Go to Step 2
2 | Test the ground circuit of the DLC for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 5 | Go to Step 3
3 | Inspect for poor connections at the DLC ground terminals and the DLC power terminals at the DLC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 5 | 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 Step 5 | --
5 | Does the scan tool power up? | Go to Diagnostic System Check - Vehicle | Go to Step 1