2007 chevy malibu.

Of those 3 codes, you should fix the random multiple misfire one first, as it could be causing the other codes to be set. The 0420 might be a bad or dirty O2 sensor (that would be the easy fix) - it might also mean the catalytic converter is going bad or an exhaust leak, but I'd start with the O2 sensor. I've read that the 0171 (lean condition) and 0300 (random misfire) has a technical service bulletin (TSB: 06-06-04-033) out on it, the suggestion was to bring it in and have the dealer reflash the computer with upgraded calibration, that would take care of both codes. I would take this back to the dealer, and inform them of the TSB above, they should take care of this for you.

Thank u. Could i replace the 02 by myself or does it require a professional

The question for you though is which sensor you need to replace, as I think there are 3 O2 sensors, one is at or near the catalytic conv, one under the exhaust manifold on the side of the engine facing the firewall, and one after the cat. The one at the exhaust manifold can be a bit of a pain to reach. They do make a special socket for it that will make your life a little easier to install it. The sensor is less than 40 and the socket is about 10. But don't jump the gun yet - most of the time O2 codes come up it doesn't mean a bad sensor, in your case it might mean the cat is bad or going bad. I jumped the gun in suggesting to clean or replace that sensor. In light of the TSB regarding those codes, you might want to take a trip to the dealer first, before deciding on replacing any parts. All 3 of those codes might in fact pertain to a bad cat.

I will make an appointment tomorrow. Thanks bud