Co2 sender for a 2006 Buick rendezvous

What is the code thats present? Iy would be very helpful to know. Just because the o2 sensor is giving a code doesnt mean it's at fault, alot of times its reporting an issue, I had a customer that though he needed a new one but after reviewing the code (bank one rich condition) we discovered that his air filter was extremely dirty! He changed and and code be gone! It just goes to show that it could cost $4 or $400