I have 2002 gle I just had the oil changed at a trust worthy shop less then 700 miles ago when the codes p0011 and p0021 came up they went away after but now I only have a p0011 can somone lend some advice as far as p0420 I was just wondering if anyone has had experience with it themselves need help fixing

 

Also to give more info the car has recently had a loss of power and doesn't get mpg it should hopefully somone out there can give me some useful advice

 

P0420 points to a problem with your Bank 1 catalytic converter. You second comment (re. lack of power), further suggests that your B1 pre-Cat may be worn out and plugged up - your car can't breath.
There are several remedies for this problem: replacing the converter, removing it, or "drilling it out". The choice depends on which state you live in (removal is illegal in NY, CA and some other states).
There are plenty of threads on the subject - just search.

 

Thank you I will look up more on this and yes I live in ny so it's a little bit tougher