Circuit Description

PCM has the ability to monitor catalyst efficiency by using HO2S1 and HO2S2. HO2S1 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 determines catalyst's ability to convert exhaust gases efficiently. If TWC is operating efficiently, HO2S1 will be far more active than HO2S2. DTC P0136 will set when:

• Maximum voltage of HO2S2 is less than 0.6 volt in closed loop mode for 8 minutes.
• Minimum voltage is 0.3 volt or greater for 5 seconds after maximum voltage check and fuel shut-off mode.