Diagnostic Circuit Check
The purpose of the Diagnostic Circuit Check is to ensure the "CHECK ENGINE" light is working, and that the ECM is working and can recognize a fault. This is the starting point for any diagnosis. If there are no trouble codes stored, see SYSTEM PERFORMANCE CHECK.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test checks the "CHECK ENGINE" light circuit. Normal response is for light to be on steadily.
- This test checks to see if the ECM can recognize a fault. When the engine is not running, there is no reference pulse and light should flash Code "12".
- This test checks if there is a problem that will set a code at curb idle for one minute.