Scan Tool Testing and Procedures

Circuit Description
There should always be a steady Malfunction Indicator Lamp (MIL) when the ignition is ON and engine OFF. Battery ignition voltage is supplied to the lamp.

The PCM will turn the lamp ON by grounding the MIL control circuit.

Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table.
2. This step verifies if the problem in the Scan tool or the vehicle.
5. If the resistance reading is below 10 ohms, this indicates that the Serial Data circuit or a Controller Module that shares the circuit is shorted to ground or shorted internally.
6. By disconnecting each Controller Module that shares the Serial Data circuit and re-checking the resistance can determine if the shared Controller Module internally.
7. This step checks to determine if the Serial Data circuit is shorted to voltage.
8. A resistance reading under 10 ohms indicates that the circuit has continuity. A high resistance reading indicates an open in the circuit.