Circuit Description
WARNING: This page is about a different car, the 2002 Pontiac Sunfire and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) supplies a voltage of about 450 millivolts between the Oxygen Sensor (O2S) 1 high signal circuit and the low signal circuit. The O2S 1 varies the voltage within a range of about 1000 millivolts if the exhaust is rich, down through about 100 millivolts if the exhaust is lean.
The sensor is like an open circuit and produces no voltage when less than 600°F (315°C). An open sensor signal circuit or a cold sensor causes an Open Loop operation.