- Powertrain/On-Board Diagnostic System Check

On-Board Diagnostic (OBD) System Check:

On-Board Diagnostic (OBD) Wiring Schematic:

CIRCUIT DESCRIPTION
The On-Board Diagnostic (OBD) system check is an organized approach to identifying a problem created by an electronic engine control system malfunction, and is the starting point for driveability complaint diagnosis. It directs the service technician to the next logical step in diagnosis. Understanding the chart and using it correctly will reduce diagnostic time and help prevent unnecessary parts replacement.

TEST DESCRIPTION Numbers below refer to circled numbers on the diagnostic chart.
1. The Malfunction Indicator Light/Service Engine Soon light (MIL/SES) should be "ON" steady with the ignition "ON" and the engine not running. This is a bulb and circuit check. If the lamp does not illuminate, the "INDIC" fuse may be open, the lamp may be burned out, there may be an open circuit to the lamp driver in the PCM (CKT 419), or there may be a problem with PCM ground circuits or the PCM itself.
2. This test ensures that the PCM is able to operate the MIL or SES light, and circuit 419 is not shorted to ground.
3. A displayed Tecch-1 parameter that is not within the typical range may indicate the area which is causing the problem.