Post O2 Oxygen Sensors
 

Is it common for the post O2 sensors to trip an SES light? My 2001 X5 4.4 threw an error this morning. I replaced the Pre Cat sensors last fall at 75K and now the truck has 80K. Other than that it is running fine.

Thanks
JD

bump - anyone ever have to replace these? I am just wondering if I might have a bigger issue with the catalytic converters. Thanks JD

Yes, post cat sensors throw codes

These post cat sensors will post codes, but as they dont' affect the performance of your vehicle, most people never bother replacing them.

As you've already changed the pre-cat ones, you should be in good shape and there is no real need to spend the money of the post cat ones.

I've replaced them. I had a blog of sorts going within my own post on this forum. Basically I was chasing down a few P codes which all pointed to my pre-cat O2s. Replaced both of those and still had an SES light come back. Replaced 1 of my post-cats after some deeper troubleshooting and it's been cured ever since.

Unfortunately, A good portion of U.S. vehicles are located in areas which require emissions inspection... vehicles will not pass with faulty post-cat sensors. Additionally, if you don't fix them, your will have a constant SES light and will never know when a "real" code appears, e.g., you'll have to do periodic OBD-II code checks if you want to know if a "real" fault has developed, e.g., if I develop an intake leak and start running lean, I would like to know there is a problem as soon as the computer detects it and turns the SES light on.

Thanks for all the responses, just ordered a set of sensors. I hope this is the problem and not the cats