Why are there two oxygen sensors on a 97 Corolla?

Answer 1

Some modern cars like the maxima even have four O2 sensors. The reason some cars have more than one O2 sensor is to be able to moniter the level of unburnt hydrocarbons that are present before the catalytic converter and the level present after the catalytic converter, this is useful for determining how efficient the catylytic converter is at burning off these unburnt hydrocarbons present in the exhaust gases. The computer is also able to use the information from multiple O2 sensors to get a clear reading of the engines air to fuel ratio so it can deliver a more precise amount of fuel to the engine.