Circuit Description

PCM has the ability to monitor efficiency of Three-Way Catalyst (TWC) by using HO2S-1 and HO2S-2. HO2S-1 produces an output signal indicating oxygen content in exhaust gases entering TWC. HO2S-2 produces an output signal indicating oxygen storage capacity of TWC. A comparison reading from HO2S-1 and HO2S-2 determines TWC's ability to convert exhaust gases efficiently. If TWC is operating efficiently, HO2S-1 will be far more active than HO2S-2.

DTC will set when:

• Average voltage of HO2S-2 is .4 volt or greater, engine speed is greater than 1600 RPM, and ECT is 158°F (70°C) or greater.
• Average voltage of HO2S-2 is .5 volt or less, engine speed is greater than 1600 RPM, and ECT is 158°F (70°C) or greater.

When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. PCM will record operating conditions at time of failure and store information in freeze frame buffer. PCM will turn HO2S-2 heater off.