obd codes and abs

i have a 2001 montana and the 1st problem is my abs light keeps comming on. i hear the abs kick in before the van even moves , i can feel it on the drivers side. can some one please tell me what to do or what to chek and my second problem, is my check engine light came on and when i hooked my obb2 code reader up i got " P0140 " and " P0141 ". it is an o2 sensor on bank 1 sensor 2, but where is that and is it easy to change.
thanks
thomas

The sensors are on the exhaust pipe. The first one is behind and below the rear exhaust manifold back by the firewall. You can see it and change it by coming up from below the engine. The second one is back by the converter and is easy to find.

I'd reset that code and see if it comes back on. The sensors should not be bad, its not a common issue unlike the abs light.

The abs problem is most likely one of the wheel sensors drifting out of acceptable range for output. The light should stay on when this happens and after the first attempt when you start the car, the abs system should not function as long as the light is on. You will need a code reader that can scan the wheel sensors to find which is the bad one.
John

I'm not sure about the P0140 code, but this helped me with the P0141 code - REMOVED BY MODERATOR

Check the wiring leading to the O2 sensor downstream from the catalytic converter. If the wiring is good, check the sensor's operation using a scope. If it's not working like it should then replace it.

can i use my multimeter to test it

can i use my multimeter to test it
No, that's not reliable. I changed one of my front hub bearings last year and the new bearing set an abs code right away. The sensor on the bad bearing (which still worked OK, just rumbled due to bad bearings) measured exactly the same as the sensor in the new bearing but still the abs code was being set. I removed the new bearing and took it back to Napa for another. The third bearing measured exactly the same as the other two but this time the abs light went out.
I used a decent fluke meter and measured both ohms of the sensor and output voltage when you spin the bearing--these looked the same on all three bearings. I think the difference must be the pulse width timing (on time vs off time) that made the abs system set the code.

You need the scanner tool to find out which of the four sensors is setting the code and then change that one. Without the scanner, you need to get lucky or change all 4.