Circuit Description

A three-way catalytic converter is used to maintain low emissions. PCM monitors exhaust gasses from converter using Bank 1 HO2S. Sensor is located in exhaust stream past three-way catalytic converter. These sensors produce an output signal which indicates oxygen capacity of catalyst. This determines catalyst's ability to convert exhaust emissions effectively.

During normal operation, Bank 1 HO2S signal will be far less active than that produced by Bank 1 HO2S 1. If a problem exists causing PCM to detect excessive Bank 1 HO2S activity outside of an acceptable range for an extended period of time, PCM will set a DTC. This indicates that three-way catalytic converter's oxygen storage capacity is less than acceptable range.

DTC will set when the following conditions are present:

• No AIR, CKP, CMP, IAT, IC, MAF, MAP, ECT, TP, EVAP, left bank HO2S, misfire, left bank fuel trim, injector, VSS, engine protection or transmission related DTCs set.
• ECT greater than 149°F (65°C).
• Vehicle speed between 20-85 MPH.
• 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 14-40 gm/s.
• Closed loop fuel control enabled.
• PCM determines oxygen storage capability of catalytic converter has degraded to less than a calibrated threshold.