Diagnostic Circuit Check
The diagnostic circuit 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 the unnecessary replacement of good parts.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Checks the CHECK ENGINE light operation.
- Checks to see if ECM's self-diagnostic mode is operating.
- Checks to see if the ECM's serial data output is operating.
- Checks to see if engine will start.
- Checks for any codes that are stored in ECM memory with engine running.
- Checks for any codes that are stored in ECM memory with engine off.
- Compares ECM's control data to typical data values.
- Checks to see if code(s) are intermittent problems.