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.
Circuit Description
Engine Control Module (ECM) compares waveform pattern of heated Air/Fuel (A/F) sensor located on exhaust pipe in front of catalytic converter with waveform pattern of heated oxygen sensor located on exhaust pipe behind catalytic converter to determine if catalytic converter performance has deteriorated. If catalytic converter is functioning properly, waveform pattern for heated oxygen sensor on exhaust pipe should switch back and forth from rich to lean more slowly than A/F sensor. If both waveform patterns switch at a similar rate, catalytic converter performance has deteriorated.
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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.