On-Board Diagnostic (OBD) System Check: Notes

The OBD System Check determines:

• If Malfunction Indicator Light (MIL) operates.
• If PCM is operating and can recognize a fault.
• If any DTCs are stored.

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS  and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the diagnostic circuit check, if no codes are indicated and driveability problems still exist, see the TESTS W/O CODES article and SCAN TOOL USAGE in the TESTS W/CODES article.

1. Check if Malfunction Indicator Light (MIL) is illuminated with engine running. Check for driveability concerns. Also, check for faulty computer-controlled components. If problem is found, go to next step.
2. Turn ignition off. Install Tech 1 scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to DLC DIAGNOSIS OR NO SCAN TOOL DATA  .
3. Crank engine. If engine cranks, go to next step. If engine does not crank, diagnose starting and charging system.
4. Turn ignition on with engine off. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to next step. If MIL does not illuminate, go to MIL DIAGNOSIS  .
5. Attempt to start engine. If engine start and runs, go to next step. If engine does not start, or starts and dies, go to NO START DIAGNOSIS  .
6. Check for any applicable technical service bulletins. Perform repairs as necessary. If no applicable bulletins are found, go to next step.
7. Using scan tool, check for Diagnostic Trouble Codes (DTCs). If DTCs are not present, go to step 9). If any DTCs are present, go to next step.
8. Using scan tool, store FREEZE FRAME data. Diagnose any stored DTC. See the TESTS W/CODES article.
9. Start engine. Observe Malfunction Indicator Light (MIL) with engine running. If MIL illuminates, go to MIL DIAGNOSIS  . If MIL does not illuminate, go to next step.
10. Compare scan tool engine data with actual control system data values. If value is within limits, see the TESTS W/O CODES article. If value is not within limits, go to the SYSTEM/COMPONENT TESTS article.