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.
OBD-II Drive Cycle & Malfunction Indicator Lamp Function
When a malfunction is present for two consecutive drive cycles, the MIL is turned on, except for steady state catalyst efficiency monitor and misfire detection monitor. The MIL is turned on for a steady state catalyst efficiency monitor malfunction after the malfunction is present for three consecutive drive cycles. When a misfire that would cause catalyst damage is detected, the MIL will turn on or flash. If the misfire is the type that will cause an emission failure or an inspection maintenance failure, the MIL Will turn on after the malfunction is detected during the next drive cycle. The MIL is turned off after three consecutive drive cycles without the same malfunction being detected provided no other DTCs are stored that would independently turn the MIL on. The actual number of drive cycles necessary to control the MIL varies with each monitor. See appropriate monitor under ON BOARD DIAGNOSTIC II MONITORS .
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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.