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.