Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
"Scan" Data Diagnostic Circuit Check
The Diagnostic Circuit Check is an organized approach to identifying a problem created by an Electronic Engine Control System (EECS) malfunction. It must be the starting point for driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint.
The "SCAN DATA" chart may be used for comparison, after completing the diagnostic circuit check and finding the on-board diagnostics functioning properly and no trouble codes displayed. The typical values are an average of display values recorded from normally operating vehicles and are intended to represent what a normally functioning system would typically display.
Only the parameters listed are used in this article for diagnosis. If a "SCAN" tester reads other parameters, the values are not recommended by General Motors for use in diagnosis.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.