Diagnostic Circuit Check
The Diagnostic Circuit Check determines if the "SERVICE ENGINE SOON" light works, the ECM is operating and can recognize a fault and if any codes are stored.
This is the starting point for any diagnosis. If no codes are indicated, see SYSTEM PERFORMANCE CHECK. If no additional checks are called out from the System Performance Check, see TROUBLE SHOOTING and SCAN TESTER USAGE in the CCC TESTS W/O CODES article in this section.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Check operation of "SERVICE ENGINE SOON" light. With key on, "Scan" tester not connected and engine not running, light should be on steady. "INTERMITTENTS" is located in CCC TESTS W/O CODES article in this section.
- Grounding "test" terminal will flash a Code 12 and any stored trouble codes. The light must go completely off to indicate a code. If light goes from bright to dim, see CHART A6 - "SES" LIGHT ON, WON'T FLASH CODE 12. This is not considered a code.
- See SCAN TESTER USAGE in the CCC TESTS W/O CODES article in this section. If "Scan" tester is not operating properly, try it on another vehicle. If it works on other vehicle, cigar lighter should be checked for battery voltage and a good ground. If "Scan" tester displays "NO DATA" or "NO ALDL" with ignition on, see CHART A6 - "SES" LIGHT ON, WON'T FLASH CODE 12.
- No codes at this point indicate the problem is intermittent and SYSTEM PERFORMANCE CHECK should be performed. If one or more codes are displayed, see appropriate trouble code chart.