Circuit Description

VCM supplies a voltage of about.45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. VCM monitors activity for 100 seconds after closed loop. During monitored period, VCM counts how often HO2S switches between rich and lean. VCM determines average switching time. If average switching time is too slow, DTC P0133 will set.

HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S is operating properly by checking response time.

For duplication of DTC, ensure:

• DTCs P0131, P0132, P0134 and P0135 are not set.
• No active EVAP system, TP, IAT, MAP, ECT, MAF sensor, misfire DTCs are set.
• No intrusive tests are in progress.
• No device control active.
• System voltage is 11.7-18 volts.
• System is in closed loop.
• Engine coolant temperature is greater than 135°F (57°C).
• Engine is running.
• MAF is 15-55 grams per second.
• Engine speed is 1100-3000 RPM.
• EVAP canister purge is enabled.