Trouble Code P0135

2000 Montana.
Engine light is on so I borrowed an OBD II reader and got the above code.
Searching trouble codes I've seen it's an o2 sensor (Bank 2, Sensor 1) - "o2 Sensor Heater Circuit Malfunction".
Sounds to me like a simple o2 sensor. Having not done anything more difficult than brakes on this particular vehicle, I have 3 questions:

Is this something a "driveway mechanic" can do?
Is there more than 1 o2 sensor?
Where is this particular sensor?

I do not have a repair manual at this point in time and I understand I ought to grab one but I've been hesitant due to what I perceive as the relative difficulty difference between my '91 Sunbird and this. If this is something I can do in the driveway, then I will grab the part and the repair manual. If not, at this moment I see no point in the repair manual (I figure most problems will be electronic and likely too much work for a non-mechanic).
Thanks for your help.

Heater circuit in the sensor in the #2 cylinder bank, first one downstream, check for 12v to the heater circuit wire with key on, check ground side of wire in the harness, if all good the sensor is bad. Sorry don't know the color codes.

It's likely a bad 02 sensor. If you are anywhere near 100k miles it's about time to replace it anyways. Its located just after the rear exhaust manifold joints the cross over pipe...so in other words right in the middle of the back of the engine. It's awkward to get to, but once you roll the engine forward and remove the coil pack, you can get to it. I did mind this way a few months ago. The other method is to go up from the bottom of the engine through the opening between the floor pan and exhaust pipe (do when things are cool...not after a long, hard drive :) ) It's tighter and my fat hands and sausage-like fingers don't fit...but yours might.

There is also a 2nd O2 sensor after the cat converter. It can go bad as well but does not enter into engine performance in any way. It's only there to measure emission efficiency.

Thx so far folks.
Rolling the engine forward is unlikely to happen for me - I don't have the equipment to move and secure it.
I've got ramps so I got under the van and could see what I think is th o2 sensor, problem is I see 2 things that may be the 02 sensor. Unless someone has a photo of this section of the van, I think I need to go get a repair manual. Which ever of the 2 items is the correct one, I'm in for a doozy - position is going to be tough to put a wrench or socket onto. Should be fun.
For kicks I'll keep posted when I get to it (combination of laziness and lack of time keeps me away from it).
Thx again.

EDIT: The one I thought was the sensor, is the sensor (cool huh?). Pain in the crack to get to without rooling the negine - but we've discussed that already. Should be simple enough, just a matter of getting the old one out - buy the special socket with the slot up the side or try to borrow one of those open-end wrench sockets that goes on a ratchet.
Should be fun, can't wait. :rolleyes:

My apologies for hijacking this thread. Would Bank1 Sensor 1 be the sensor between the Cat Converter and the Muffler?

I had PO135 for B1S1, last night I replaced that sensor. I'm hoping I got the right one. Had AZ clear the codes on the way home from church this morning.

Note this is for '01 Montana.

Probably a little late as I imagine you've already got your answer (if trouble light hasn't come on again, you're likely good).

I would assume you are correct - b1s1 must be post-cat.

My code disappeared after a long drive on the highway (pure accident - didn't intend to clear it that way) and it hasn't come on since. Nice $90 save.