Right Rear O2 sensor
 

My car seems to like to eat rear O2 sensors.
I have had to replace 3 of them now. One OEM, and 2 aftermarket. What is causing them to fail? Should I change the front as well? Fuel economy is unchanged and the car runs great.

How do you know they're failing?

I get a trouble code for the right rear O2 sensor. If I clear the code and drive the car, it comes right back. After installing a new sensor, it will be fine for about 6 months, then back to the same thing.

Does Mercedes have a thing in that if they install a part it is guaranteed for two years? If so, bite the bullet and let them fix it and have them replace the sensor every six months until they find the real problem.
Mike T.

Trouble with that is that I live 225 miles from the nearest dealer. I could buy a 5 year supply of sensors for what it would cost to have the dealership do one.

The easiest thing to do would be to disable the secondary bank of O2 sensors.
They are not necessary for emissions.

Disabling done via SDS/Star

I wonder if my Auto Enginuity has that capability.

The downstream sensors shouldn't be going. They usually indicate the cat is bad. I would change the upstream ones first. What code are you getting? Maybe it's the brand of sensor you're installing. Which one is it? Maybe pick up an O2 sensor from FCPeuro and have it replaced under their lifetime warranty.

The downstream ones basically monitor the exhaust to make sure the cats are working. You should try doing some trouble shooting to see what else could be causing it. Usually exhaust leaks or a vacuum leak are common causes or maybe MAF or other sensors.

Just to update you guys.
This time it was the left rear O2 sensor. That's odd because last time I changed them both.
I ordered all 4 this time from FCP Euro. It's been below zero here and my heated shop is full of antique cars. The battery in my laptop is done so getting data logs is kinda tough.