2002 Grand Prix GTP has code p1133. Insufician swtching bank 1 sensor 1 . What should I do, Replace it?

SOURCE: 2002 Pontac Grand Prix GTP P0171 code engine stumbling at times

Bank 1 is the frt side exhaust manifold (did they say bank 1 sensor 1?),you can start by replacing that sensor,i would check the intake for leaks ,the gm 6cly. are known for bad intake gaskets,you will see oil coming out form the frt or rear of the intake,also check your atifreeze overflow bottle for bronwish sludge,which means that the oil is mixing with the antifreeze.A leaking intake could cause that lean condition.

SOURCE: Where is the 02 sensor located in a 2002 Pontiac

The O2 sensors are located in the exhaust pipe between the exhaust manifold and the catalytic converter. When it's referring to a bank number, it's talking about which set of cylinders. I'm assuming that you have a v-6, if it's specifying a bank. Either way, There are two O2 sensors, one for each side of the engine, and you'll want to replace both, since whatever made the one go bad has probably done the same for the other side too. Anyways, it looks like a spark plug with 4 wires coming out the top screwed into your exhaust pipe. If you follow the exhaust from the engine, you will find your sensors. Hope this helped, and good luck.

SOURCE: Obd code reads P1133. Replaced sensor 1 bank 1

What you need to do. is use the codes you get ,to look at a diagnostic chart,of possible causes for the codes.
If it is an O2 or any other sensor, you should perform some type of test,to determine,not only if their not working correctly,but what the system problem is ,that set the codes.
OBD2 Codes-do not tell you what to replace. They indicate a system malfunction. It is up to you to diagnose the issues.

If you believe you have a downstream O2 Sensor going,you most likely have a cat not far behind or it wouldn't be out of range and set the code

I would install a new cat and both sensors,on a 13 year old vehicle