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 oxygen sensor (bank No. 1 sensor No. 1) located on driver's side exhaust manifold with waveform pattern of heated oxygen sensor (bank No. 1 sensor No. 2) located on driver's side 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 (bank No. 1 sensor No. 2) should switch back and forth from rich to lean more slowly than heated oxygen sensor (bank No. 1 sensor No. 1). If both waveform patterns switch at a similar rate, catalytic converter performance has deteriorated. DTC is set when heated oxygen sensor (bank No. 1 sensor No. 1) and heated oxygen sensor (bank No. 1 sensor No. 2) have nearly the same waveform pattern after engine and catalytic converter are at normal operating temperature and vehicle is driven. Possible causes are:
- Exhaust system leak.
- Defective heated oxygen sensor.
- Defective catalytic converter.
NO RELATED
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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.