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 the 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 to prevent erroneous detection, and ensure a thorough malfunction detection. By switching the engine control module (ECM) to check mode when trouble shooting, the technician can cause the malfunction indicator light (MIL) to illuminate for a malfunction that is only detected once or momentarily (hand-held tester only). See CHECK MODE CODE RETRIEVAL (TOYOTA HAND-HELD TESTER ONLY) under RETRIEVING DIAGNOSTIC TROUBLE CODES. When a malfunction is first detected, the pending fault code is temporarily stored in the ECM memory (1st trip). If the same malfunction is detected again during the second drive test, this second detection causes the MIL to illuminate (2nd trip). However, the ignition switch must be turned OFF between the 1st trip and 2nd trip.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.