Circuit Description

VCM supplies a voltage of about.45 volt between HO2S 1 signal and HO2S 1 ground circuits. HO2S 1 varies voltage from about one volt with rich exhaust to.1 volt with lean exhaust. VCM monitors activity for 100 seconds after closed loop. During monitored period, VCM counts how often HO2S 1 switches between rich and lean. VCM determines average switching time. If average switching time is too slow, DTC P0153 will set.

HO2S 1 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). HO2S 1 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 1 is operating properly by checking response time.

For duplication of DTC, ensure:

• No active EVAP system, misfire, ECT, IAT, MAF, MAP or TP sensor DTCs are set.
• No intrusive tests are in progress.
• No device controls are active.
• System voltage is greater than 9 volts.
• DTCs P0131, P0132, P0134, P0135, P0151, P0152, P0154 and P0155 are not set.
• System is in closed loop.
• Engine coolant temperature is greater than 135°F (57°C).
• Engine is running.
• MAF is 15-55 gm/s.
• Engine speed is 1100-3000 RPM.
• EVAP canister purge is enabled.