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.
Two-Trip Detection Logic
The diagnosis system operates in normal mode during normal vehicle use. It also has a check mode for technicians to simulate malfunction symptoms and trouble shoot. Most DTCs use 2 trip detection logic (when a malfunction is first detected, malfunction is temporarily stored in ECM memory, 1st trip) to prevent erroneous detection, which ensures malfunction detection. By switching ECM to check mode when trouble shooting, technician can cause MIL to light up for a malfunction that is only detected once or momentarily (hand-held tester only). See NORMAL MODE CODE RETRIEVAL under RETRIEVING DIAGNOSTIC TROUBLE CODES.
If same malfunction is detected again during second drive test, this second detection causes MIL to light up (2nd trip). However, ignition switch must be turned OFF between 1st trip and 2nd trip.
Use the Manual With the Right Hardware
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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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