Diagnostics: OBD II Scan Tools

A mechanic using two OBD 2 scan tools.

Use a scan tool to monitor sensor input from the onboard computers. Many scanners can also actuate items in mode 8, bypassing sensor input. If the vehicle is overheating, and the ECT or engine coolant temperature sensor is suspected, bypass the sensor and activate the fan circuit with the scan tool. If the fan works, inspect the ECT and associated circuitry.

Scan Tool Tips

The same is true for the fuel-sending unit. If the gauge is continuously reading full or empty, connect the appropriate scan tool to the DLC and monitor the fuel level sensor's input to the PCM while adding fuel to the tank. This test indicates if the sending unit is functioning correctly or if there is a problem with the instrument panel gauge or circuitry.