97 RAM Oxygen Sensor

Is there anyway to determine which Oxygen sensor is bad? I know one of them is bad... just don't know which one. I know this because my mechanic hooked it up to his computer the other day, but he didn't tell me which one it was. Apparently my 97 RAM has 3... a left and right bank and one after the catalytic converter. I would rather replace this myself without having to take it back to the mechanic. Thanks

Oh in case it makes a difference I have a 97 RAM 1500 extended cab, 318, automatic, w/AC

look here i have the same truck with the same problem

http://www.automotiveforums.com/vbulletin/showthread.php?t=275104