- Powertrain/On-Board Diagnostic System Check

Tech-1 Diagnostic System Check:

PCM Power Feed, MIL Lamp, & Diagnostic Circuit Schematic:

CIRCUIT DESCRIPTION
The on-board diagnostic system check must be the starting point for any driveability complaint diagnosis Before using this you should perform a careful visual/physical check of the PCM and engine grounds for being clean and tight.

The on-board diagnostic system check is an organized approach to identifying a problem created by an electronic engine control system malfunction because it directs the service technician to the next logical step in diagnosing the complaint.

TEST DESCRIPTION
Numbers below refer to circled numbers in flow chart.
1. The MIL (Service Engine Soon) should be "ON" steady with the key "ON" and engine not running.
2. This test ensures that the PCM is capable of controlling the MIL properly, and that circuit 419 (lamp driver circuit) is not shorted to ground. The Tech 1 "Misc. Tests" lamp control function overrides the normal PCM controlled state of the lamp, allowing the lamp to be turned "OFF" with the key "ON", engine not running.
3. Scan tool data not within normal range may indicate a problem with an associated circuit, sensor, or component.