- Powertrain/On-Board Diagnostic System Check

Flow Of Diagnosis:

PCM Indicator Circuit:

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. It must be the starting point for any driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint. Understanding the flow chart in the accompanying image and using it correctly will reduce diagnostic time and prevent the unnecessary replacement of good parts.

PRELIMINARY DIAGNOSTIC STEPS
1. Obtain an accurate description of the complaint and verify. Include completing the Driveability Worksheet and Vehicle Repair History. Refer to Technical Management Support/Vehicle Inspection Forms for these worksheets.

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 - Programable Read Only Memory

NOTES ON CHART 1
1. Checking if vehicle will enter diagnostics. If it will not, then there is an on-board diagnostic system fault that can be diagnosed by using the Self-Diagnostic System Check. Testing and Inspection

2. Checking to see if the Instrument Panel Cluster (IPC) is able to communicate with the Powertrain Control Module (PCM). If it is not, Code I034 will set or "NO PCM DATA" message will be displayed when using diagnostics.

3. "Service Engine Soon" Malfunction Indicator Lamp (MIL) should be "ON" when vehicle is in diagnostic mode.

4. Checking if powertrain system is operational.

5. Checking for PCM codes set that should be diagnosed.

6. "Service Engine Soon" MIL should be "OFF" with no codes set.

7. Checking if a known customer complaint is causing the problem.

8. If your complaint is not in the customer complaint list, perform the system check which best applies to your situation.