I recently did a diagnostics code check on my 97 dodge neon dohc and I got the code 21 three times, I know what it means but why would I get it three times and where would I be able to locate my 02 sensor? I also got the code 17 I am not sure why I am getting this code, if anyone could help me out this would be great. Thanks :)

why would I get it three times and where would I be able to locate my 02 sensor?It just means it found the problem on 3 different occasions. It is normal. You have two 02 sensors, upstream and downstream. The downstream is located right in front of your catalytic converter and the upstream is above the passenger side axle.

The code 17 means your car did not come up tp operating temp within an acceptable time limit.