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.1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

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 or HO2S circuit is open. DTC P0134 will set if VCM fails to detect minimum number of HO2S 1 voltage transitions greater than and less than bias voltage range of 300-600 mV.

For duplication of DTC, ensure:

• DTC P0135 is not set.
• No active EVAP system, misfire, TP, IAT, MAP, ECT or MAF sensor DTCs are set.
• No intrusive tests are in progress.
• No device controls are active.
• System voltage is 11.7-18 volts.
• Engine run time is greater than 2 minutes.
• Decel fuel cut-off mode is not active.
• ECT is 137°F (58.5°C) or greater.
• MAF is 13 grams per second.
• System is in closed loop.