For Using OBD II Scan Tool Or Hand-Held Tester

WARNING: This page is about a different car, the 2005 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.

Before using the scan tool or tester, the scan tool's instruction book or tester's operator manual should be read thoroughly.
If the scan tool or tester cannot communicate with the ECU controlled systems when you have connected the cable of the tester to the DLC3 with the ignition switch and tester turned ON, there is a problem on the vehicle side or tester side.
1. If communication is normal when the tester is connected to another vehicle, inspect the diagnosis data link line (Bus(+)line) or ECU power circuit of the vehicle.
2. If communication is still impossible when the tester is connected to another vehicle, the problem is probably in the tester itself. So perform the Self Test procedures outlined in the Tester Operator's Manual.