OBD System Check: Notes

On-Board Diagnostic (OBD) System Check is an organized approach in identifying a problem created by an electronic engine 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 a complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent unnecessary replacement of good parts.

1. Checks Malfunction Indicator Light (MIL) operation.
2. Checks if ECM's self-diagnostic mode is operating.
3. Checks if ECM's serial data output is operating.
4. Checks if engine will start.
5. Checks for DTCs that are stored in ECM memory with engine running.
6. Checks for DTCs that are stored in ECM memory with engine off. If no DTCs are set and engine won't start, go to appropriate CHART A1-3 in BASIC TESTING - 1.3L 4-CYL article.
7. Compares ECM's control data to typical data values.
8. Checks if DTCs are intermittent malfunctions.