[kszygc]

I got this in reply to my ? about them.

Quote:
Originally Posted by kszygc
Once a year or so I have to replace the downstream O2 sensors on a 99 Silverado. By that I mean the 2 sensors after the converter not the two before. It has the 5.3 w/ auto trans, auto 4x4. The previous owner cut the y-pipe and installed 2.25 inch pipe all the way to the rear without mufflers at all. I bolted on a pair of 4 inch supertrapps at the back end to cut down on my hearing loss, it's bad enough as it is. It has a K&N fitercharger kit and unknown brand of shorty headers. The computer is still stock though. I will get the DTC for low volts and no volts so I pull the sensor and it is in pieces internally. They aren't terribly expensive, I just get tired of replacing them. Anybody have any ideas or experience?

So I'm guessing you have 2 pipes one on each side, from the maniflod to the rear. Correct? If it is then I would put the 2 new downstreams in, and feel how much vibration is around them, if there is alot that could explain the internal pieces being broke. To fix that you could tac a hanger close to each pipe leaveing room to R&R the o2s if they go bad in the future. If possible use those hangers that have rubber straps on them to allow movement.

From what I researched for your codes, I'm not sure, are the sensors broken up internally? It sounds like the sensors is not switching over. It could be a bad sensor, even if it's not broken up, and it's just not responding. that would be my first guess. On the other hand, I've been also told that a bad burn in the combustion chamber can cause issues as well. Several other options come to mind but I doubt that two downstreams sensors are bad. Possibly the one you changed was bad from the factory. Can you swap from left to right on the downstream side? the upstream sensor could have been damaged by heat, vibration, or welding gases or slag. Once again, maybe clear them and swap the upstream sensors after proving the downstream ones. good luck