Diagnostic Circuit Check (Except ECM/BCM Equipped Vehicles): Notes

The Diagnostic Circuit Check determines:

• If SERVICE ENGINE SOON light works.
• If ECM is operating and can recognize a fault.
• If any codes 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 TESTS W/O CODES article and SCAN TESTER USAGE in appropriate TESTS W/CODES - 3.8L PFI article.