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Submitted by tallenml350 on May 10, 2020

I have a 2011 Mercedes Benz ML350 4Matic. The code says it's the driver side upstream o2 sensor. I tried to access it from the top as well as from underneath. Underneath I can barely get my arm between the transmission and the transfer case with no room to work a ratchet. Up top is far away and no room to work a ratchet. How do I remove the o2 sensor? Will taking the drive shaft off help? Is it best to go from up top, underneath or thru the wheel well? Do I remove the heat shields? I cannot find a video showing how to remove the driver side upstream o2 sensor on this year and model. Thanks.



You have an ML350, so you should be able to get under it without jacking the car up.  If it's the upstream sensor, you should be able to it from the top this way.  There are specific style sockets for removing an o2 sensor, so you'll need one of those.  Next, take a very long ratcheting wrench or breaker bar, put the socket on it, and start loosening the sensor.  Those also like to swell up and seize in the converter, so you may need to heat it to get it out or soak it in PB Blaster to loosen the bolt.  Only spray it when the engine is cold.  The new sensor is going in the same way the old one comes out, so be careful not to break the old one off in the converter.  That's the only way I can think of to do the sensor from the top; it might take a while, but it's easier than lying on your back and snaking your arm up and over the transfer case and converter.