trouble codes P0133 and P0171
PO133 is an O2/oxygen sensor trouble code. This code in particular states that the oxygen sensor is responding to the exhaust running through the system and out your tailpipe much too slowly. This more than likely means that the sensor is bad, or at least extremely close to it. Either way, they are cheap parts and easy to R & R for most makes and models.
PO171 Ok, this one is a bit more complex and troublesome. This code reads that the fuel system trim is running too lean on bank 1.
Bank 1 Bank 2, ect. Are just the multiple areas of a vehicle's systems that are being monitored, to be able to collect the most accurate data.
This code basically means, something is causing the air to fuel ration on your vehicle's engine to fluctuate and make the engine begin to to burn less fuel per cylinder fire than what is required for normal, efficient engine operation. To me, this makes a lot of sense to see this code come up, because of the previous code that stated the oxygen sensor was responding slowly. And is also more than likely the reason that the O2 sensor is either, fouled now, or is very very close to it.
whatever the reason is behind the lean fuel problem is likely the cause of the oxygen sensor code as well. However, I would go ahead and replace the oxygen sensor anyways. They are cheap, easy to remove and reinstall, and they can also cause some really weird symptoms, and make your vehicle run like crap when it does go completetly bad. No more then what they cost at the part store, you'll only be doing yourself a favor regardless. If nothing else, a little preventative maintenance never hurt anyone, or any piece of equipment.