98 5.2L Ram 1500 O2 upstream sensor problem

I got the dreaded "check engine" light about 3 weeks ago. Found that it was code P0138 - upstream 02 sensor. Replaced it with a Bosch sensor and had code reset. All was fine until today. Now the check eng. light is back on and it is giving the same code. I pulled the battery cable to reset it and continued driving the rest of the night, but it came back on after a few minutes of driving. Is there something in the system that causes these sensors to go bad?? I read in a previous post that you should replace both sensors at the same time. Why? Any info. on this would be appreciated, thanks!

I got the dreaded "check engine" light about 3 weeks ago. Found that it was code P0138 - upstream 02 sensor. Replaced it with a Bosch sensor and had code reset. All was fine until today. Now the check eng. light is back on and it is giving the same code. I pulled the battery cable to reset it and continued driving the rest of the night, but it came back on after a few minutes of driving. Is there something in the system that causes these sensors to go bad?? I read in a previous post that you should replace both sensors at the same time. Why? Any info. on this would be appreciated, thanks!

I've got a 2002 Ram and had a similar problem. Mine is an automatic. I was traveling the Blueridge Parkway, decending the mountain roads. The owner's manual recommends down shifting when decending steep grades. I would routinely do so with a standard and did the same with my automatic, shifting from 3rd to 2nd. After decending for a significant period of time, the check engine light came on. The code was that of one of the two oxygen sensors. I took it to the dealer, who replaced it for about $130.00. Later, while talking to a friend of mine, he told me when the check engine light comes on and it identifies a problem; it does not say to replace that part, it just alerts you to a problem concerning that part. He went on to say generally, the enging/computer will correct itself. When this happened again, as I was decending a steep grade, I did not replace the oxygen sensor;. It went off and cleared itself after about 3 days of normal driving. I do not know the reason your check engine light came on; but if it came on as mine did, it probably is not a cause for concern. Recently, I had a code of P0304, which told me there was a problem with, among other things, the firing of the #4 spark plug. I removed the plug, re-gaped it and the code went away, however, it was still in the computer. Today, I pulled all the plugs and re-gaped them. The code cleared itself. As for replacing both sensors, my guess would be to be certain you fixed the problem, while one may be bad, the other may be on its way to going out. However, I am not a mechanic, just an average guy. This has been my experience. I hope it helps you.

Mike

You've might have been given a wrong sensor when you purchased it. Did you purchase the part from a store you go to alot ? Different sensors, different calibrations for different cars. Also, don't mix up the pre- and post sensors.