- Powertrain/On-Board Diagnostic System Check

On Board Diagnostic System Check:

On Board Diagnostic Circuit:

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:

NOTE:
a. Numbers below refer to circled numbers in flow chart.
b. Since this is the starting point for all diagnostic procedures or finding the cause of an emissions test failure, always begin here and always follow the flow chart as directed.
c. For trouble code diagnosis and Charts A-1 and A-2, see "COMPUTERS AND CONTROL SYSTEMS/TESTING AND INSPECTION/PROCEDURES/DIAGNOSTIC CHARTS Testing and Inspection

1. Get an accurate description of the complaint and verify. Include filling out the DRIVEABILITY WORKSHEET and VEHICLE REPAIR HISTORY. Refer to INFO TYPE/TECHNICAL MANAGEMENT SUPPORT for forms.

Perform Underhood Inspection:

a. Check vacuum hoses for splits, kinks, and proper routing.
b. Check ignition wires for cracking, hardness, and proper connections at both the distributor and spark plugs.
c. Check all wiring for proper connections, pinches, and cuts.
d. Check wiring harness for proper routing.
e. Check for missing components.

2. Check for manual updates, testing procedures, warranty and recall information.

3. Refer to PROM I.D.




4. The MIL (Service Engine Soon) should be "ON" steady with the key "ON" and engine not running.

5. This test ensures that the PCM is capable of controlling the MIL properly. 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.

6. Scan tool data not within normal range may indicate a problem with an associated circuit, sensor, or component.