I recently bought a new engine (2.0L SOHC) for my 2000 Neon, and I believe the motor was from an 04 or an 05 and the sensor in the back, which correct me if I'm wrong is the O2 sensor by the catalytic converter. The plugs are similar but different enough to not plug in. I am guessing the sensor changed for the newer year but I don't know, help!

 

You'll have to get the o2 censor for the motor year you had.