2001 Regal LS oxygen sensor

This is just a general info question, but can an oxygen sensor that needs to be replaced affect a cars effective M.P.G.? In other words, can a bad oxygen sensor make you burn fuel faster and not get as much out of a fill up?

Correct. The front 02 sensor is used by the PCM - computer to control the air/fuel mixture ratio for the fuel injection system in the closed loop mode of operation. Helps control the short and long term fuel trims by keeping it at the ideal 14.7:1 ratio. When they get carboned up or lazy it will affect fuel economy mainly at highway speeds, cruising or at idle once the engine has reached proper operating temperature. The rear post CAT 02 sensor is used to monitor CAT converter efficiency only.

OK....that's about what I was thinking was happeneing. Is it fairly easy to replace this sensor? I have one of the Chilton's repair manuals, but I actually haven't been able to find the sensor itself based on the pictures the manual provides.

The sensor is located on the rear exhaust manifold towards the firewall. Easy to replace with a universal 02 sensor socket and 3/8" or 1/2" drive ratchet.