Scan Tool Testing and Procedures

Data Link Connector Diagnosis (Part 1 Of 2):

Data Link Connector Diagnosis (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
There should always be a steady Malfunction Indicator Lamp (MIL) when the ignition is ON and the engine is 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 numbers below refer to the step numbers on the diagnostic table.
2. This step verifies if the problem is 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 a shared controller module is shorted internally.
7. This step checks the Serial Data circuit for a short 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.