2007 Chevrolet Impala check engine light says on

Did you get a code #? There are several 02 sensor codes, 02 performance codes, 02 circuit codes? If the 02 sensor is showing rich, could be, vacuum leak-- 02 sensor or sensor circuit problem, fuel injector problem, something like that.

the code was 171

That is lean fuel trim code. You could try cleaning the maf sensor, see if it will help. The air filter clean? Check fuel pressure. You might have a clogged fuel injector?

There is a long list of possibilities, could be a vacuum leak, somewhere?

Sorry the code was 172 rich reading could this also mean serious engine problems

I'd use a gage and check proper fuel pressure. If you don't have a fuel pressure gage, some of the national brand auto stores will loan out a fuel pressure gage. You may have to put up a deposit, but, you get it back when you return the tool.

Not only check correct fuel pressure, see if pressure holds for a bit with everything off.

Ok will do thanks what should the pressure be is it possible that the pressure is to high if is what should I do to correct it

If pressure is too high, replace fuel pump module. My info says you have a returnless fuel system, pressure regulator and filter are at the fuel pump module. Fuel pressure is 56--62psi.

Ok thanks one last question if the pressure is correct what should I do next

I'd have to see what 02 sensor is doing.

ok

Just go one step at a time, I certainly don't know everything, far from it.

Just to add, don't worry about all the possibilities, just take a basic step, checking fuel pressure, plus, see if it will hold for a bit with everything off. Go from there.