Disconnect scan tool from Data Link Connector (DLC). Connect test light between ground and DLC terminal No. 16 (Orange wire). See Fig 1. If test light illuminates, go to next step. If test light does not illuminate, repair open or short to ground in Orange wire between DLC terminal No. 16 and BODY fuse (10-amp) located in instrument panel fuse block. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. After repairs, recheck scan tool operation.
Connect test light between DLC terminals No. 4 (Black wire) and No. 16 (Orange wire). If test light illuminates, go to next step. If test light does not illuminate, repair open in Black wire between DLC terminal No. 4 and ground. See GROUND DISTRIBUTION article in WIRING DIAGRAMS.
Connect test light between DLC terminals No. 5 (Black wire) and No. 16 (Orange wire). If test light illuminates, go to next step. If test light does not illuminate, repair open in Black wire between DLC terminal No. 5 and ground. See GROUND DISTRIBUTION article in WIRING DIAGRAMS.
Check for poor connections between scan tool and DLC terminals No. 4 and 5 (Black wires) and No. 16 (Orange wire). Repair as necessary. If DLC connections are okay, go to next step.
Scan tool may be malfunctioning. Check scan tool manual for diagnostic procedures. If necessary, substitute a known-good scan tool.

Fig 1: Identifying Data Link Connector (DLC) Terminals

Courtesy of GENERAL MOTORS CORP.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Test A: Scan Tool Does Not Power Up