2004 o2 Sensor needs replacing AGAIN!!!

I have a 2004 Pontiac Montana, the check engine light came on 2 days after I bought it. It was an o2 sensor. 4-5 months later it went again and the Dealer fixed it again, then again last month, and now its the o2 sensor AGAIN!!! Is there something that could be causing this, besides the sensor itself? Is this common and have you heard of this happening before 3.4 engine (4 times?)
Thank you :confused:

I have a 2004 Pontiac Montana, the check engine light came on 2 days after I bought it. It was an o2 sensor. 4-5 months later it went again and the Dealer fixed it again, then again last month, and now its the o2 sensor AGAIN!!! Is there something that could be causing this, besides the sensor itself? Is this common and have you heard of this happening before 3.4 engine (4 times?)
Thank you :confused:

Please post the code number. (Eg.PO123) The O2 sensors relate to the emissions systems.

We'll have a better perspective on the problem with the correct code.

Also, has there been any recent work done to the van?

The code is P0140 Bank 1 sensor 2 (no activity). The gas mileage is terrible also. This has been ongoing since I bought the van March 2008. No other problems with the van. :disappoin

I have an 03 Montana.
My error code is this:
P0135 Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
Where is the sensor located. I can't find it.
Thanks,
WillieBruce

Welcome to AF, look at the rear engine pipe from the exh manifold you will see the sensor, bend over the engine from the engine compt.

It's going to be impossible to see the o2 sensor from the top side of the engine, as the cowl is in the way. You can see it from under the van, Maxwedge is correct that it is in the exhaust manifold on the back side of the engine. You have to reach up from beside the exhaust pipe to get to it.

Use good light & mirror todo a visual inspection on HO2 sensor wires, it could of got burnt, and shorted out on the exhaust manifold.,

Thanks guys. I should be able to find it with your helping. Now I need a warm day in NC in January. Not for a while!!
WillieBruce