Circuit Description

PCM has the ability to monitor catalyst efficiency by using O2S1 and HO2S2. O2S1 produces an output signal indicating oxygen content in exhaust gases entering TWC. HO2S2 produces an output signal indicating oxygen storage capacity of TWC. A comparison reading from sensors determine catalyst's ability to convert exhaust gases efficiently. If TWC is operating efficiently, O2S1 will be far more active than HO2S2. DTC P0136 will set when:

• Maximum voltage of HO2S2 is 0.4 volt or less with engine speed greater than 1600 RPM, and coolant temperature 158°F (70°C) or more.
• Minimum voltage of HO2S2 is 0.5 volt or more with engine speed greater than 1600 RPM, and coolant temperature 158°F (70°C) or more.