If scan tool displays UNABLE TO CONNECT TO VEHICLE when scan tool is connected, try scan tool on another vehicle. If scan tool operates on another vehicle, go to next step. If scan tool does not operate on another vehicle, problem is probably with scan tool.
Check DLC No. 3 for loose or damaged terminals. Ensure DLC No. 3 terminals are in correct position in connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If connector and terminals are okay, go to next step.
Check voltage and resistance between ground and specified terminal on DLC No. 3. See DLC NO. 3 VOLTAGE & RESISTANCE SPECIFICATIONS table. See Fig 1. If voltage and resistance readings are not as specified, check wiring circuit. See appropriate wiring diagram in WIRING DIAGRAMS article.

DLC NO. 3 VOLTAGE & RESISTANCE SPECIFICATIONS

Terminal No. (Circuit) ⁽¹⁾

Specification

4 (Chassis Ground)

Less Than One Ohm

5 (Signal Ground)

Less Than One Ohm

16 (Battery Voltage)

9-14 Volts

⁽¹⁾	Terminal No. 2 (Celica and RAV4) or No. 7 (all other models) provides a pulse generation during information transmission (BUS communication) from Engine Control Module (ECM).

Fig 1: Identifying DLC No. 3 Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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

DLC No. 3 Inspection