Heated Oxygen Sensor No. 1

Heated Oxygen Sensor (HO2S) No. 1 is mounted in exhaust manifold in front of catalytic converter. HO2S No. 1 produces 0.1-0.9 volt when exhaust system temperatures are greater than 600°F (316°C). ECM uses HO2S No.1 voltage to determine exhaust gas oxygen concentration during engine operation. Low voltage indicates a lean exhaust mixture and a higher voltage indicates a rich exhaust mixture. HO2S No.1 works similar to a non-heated sensor, except HO2S No.1 is heated to operating temperatures to allow system to quickly enter closed loop operation.