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.
Section 122 (Engine Controls - Basic Diagnostic Procedures): Introduction
The following diagnostic steps will help prevent overlooking a simple problem. The first step in diagnosing any driveability problem is verifying the symptom(s) with a test drive under the conditions the problem reportedly occurred.
Before proceeding with diagnostics, check for applicable Technical Service Bulletins (TSBs). If there are no applicable TSBs, perform QUICK TEST under SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE to identify Diagnostic Trouble Codes (DTCs). If no DTCs are present or only pass codes are found during self-diagnostics and symptom is present, proceed to TROUBLE SHOOTING - NO CODES - EEC-V - CNG, FLEX-FUEL & GASOLINE article for diagnosis by symptom.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.
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