getting code P0155, what could be the cause

It is your Bank 2 Sensor 1 Heater circuit in the exhaust. Unplug the O2 sensor on bank 2 (the opposite side of the the engine from cylinder 1) sensor 1 (before the catalytic converter). Looking at the O2 sensor plug, there will be usually 4 wires on a heated O2. Find the two wires that are the same color. That is your heater circuit in the O2. Using an multimeter, check the ohms through those two wires. It should be 3-5 ohms typically. If it is "infinite", "overload", higher than 20 ohms or 0 ohms, replace the O2 sensor. If you measure 3-5 ohms, you may have a wiring problem that will need to be investigated further with a wiring diagram.

You could just read all live O2 sensor data on your scanner! .. Oh, no scanner? .. If not equipped to do testing, suggest having it done before parts replacement.. As stated, it's a couple possibilities. Usually O2 sensor replacement will take care of this BUT.. Maybe not. (Passenger side is bank 2..) Obvoiusly 4.3L engine... Always a good idea to post that info when inquiring about a problem, no matter what! .. 2003 S-10 don't cut it.. S-10 what?