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. 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  .
2. 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  .
3. Using scan tool, select DTC, DTC INFO and LAST TST FAIL function. If any DTC is stored, go to step 5). If no DTCs are stored, go to next step.
4. Using scan tool, select DTC, DTC INFO and HISTORY function. If no DTCs are stored, go to step 6). If any DTC is stored, go to next step.
5. Using scan tool, save freeze frame and fail record information using CAPTURE INFO feature. If any DTC is indicated as last test failed, diagnose DTC. See the TESTS W/CODES article.
6. 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.