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
A Three-Way Catalytic (TWC) converter is used to maintain low emissions. PCM monitors exhaust gasses from converter using Bank 2 HO2S 2 located in exhaust stream past TWC converter. These sensors produce an output signal which indicates oxygen capacity of catalyst. This determines catalysts ability to convert exhaust emissions effectively.
During normal operation Bank 2 HO2S 2 signal will be far less active than that produced by Bank 2 HO2S 1. If a problem exists causing PCM to detect excessive Bank 2 HO2S 2 activity outside of an acceptable range for an extended period of time, PCM will set a DTC. This indicates that 3-way catalytic converter's oxygen storage capacity is less than acceptable range.
DTC will set when following conditions are present:
- No AIR, CKP, CMP, ECT, engine protection, IAT, IC, injector, left bank HO2S, MAF, MAP, misfire, right bank fuel trim or transmission DTCs set.
- Engine operating.
- ECT greater than 149°F (65°C).
- IAT greater than -22°F (-30°C).
- TP sensor angle greater than 2 percent.
- Engine speed 800-3000 RPM.
- MAP 25-80 kPa.
- Engine airflow between 14-40 gm/s.
- Fuel system in closed loop fuel control.
- PCM determines oxygen storage capability of catalytic converter has degraded to less than calibrated threshold.
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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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