Further research of my check engine light
 

Using my electronic device, I found that the cause of the CEL is PO150 02 sensor in
"Bank 2 - sensor 1"

How do I determine exactly which sensor this is on the ML 320- in order to replace it properly??

Also, do I really need a special tool to remove the sensor or can I do it with the proper socket??

Bank 2, so cylinders 4,5, and 6

Sensor 1, so the upstream, or pre-cat sensor

A normal wrench will usually fit (22mm or 7/8"), sockets have a hard time dealing with the wiring coming out of the sensor. You can jam one on for removal of a bad sensor, but you wouldn't want to do that with a new sensor.

MV

before removing said sensor which is located on the driverside of the car before the cat - have it tested for signal.

I say this because if you have an exhaust leak near it the sensor code will be set.

O2 sensors require a special tool. Somewhat like a socket except there is a cut out portion to feed the connecting cable thru. You can often make due with a crows-foot style wrench. Without the right tool you risk damaging the cable during reinstallation. O2 sensors are a 100K mile service item.

Bank 2 is the driver's side.

I have not done this on an ML, but on the sedans a dedicated O2 socket is required, unless you are going to drop the exhaust. As noted, it is deeper than a normal deep socket and has a cutout on the side so you don't damage the wire. You can get one at any auto parts store or online, of course.

Good luck.