I have a 2012 W166 (ML350) gasser 4Matic and I need to service the fuel filter and fuel pump. I know they are under the rear seat and I know the seat back needs to be removed to pull back the carpet to access them. Tried to remove the seats last night with no luck. There are three visible fasteners on the double wide side (drivers) and two on the single seat (passenger side). After removing them, the seat backs will still not budge. Can someone tell me where the other hidden fasteners are and if you have any tips to remove the seat backs? Thank you.

 

I only had a few minutes to look at it last night, but I discovered there are additional fasteners you can access through the rear cargo compartment. The cargo compartment floor covering the spare tire is easily removed and then you can see the additional fasteners. I will pursue removing the seats tonight and will take pictures to post here.

 

OK. I was able to completely remove the rear seats. It's very simple once you know how to access the rear bolts. In the process, I discovered why there are no DIY tutorials on how to change the fuel filter or fuel pump on a W166 (even though there are plenty on W163, W164 and other models). It is because you cannot access the fuel filter and fuel pump through ports under the rear seat. You have to drop the tank. To drop the tank, evidently you have to remove at least part of the exhaust system and the driveshaft. This job was above my capabilities so the vehicle is at my local dealer for repair as I type this.

Anyway, here are some pics to explain the process. I marked bolts with yellow masking tape becasue I am not good at adding arrows with photo editing applications:

Here are the three bolts you need to remove on the 60 (driver's side)seat:


To access the rear seat bolts, you need to remove the cargo hold downs directly behind the seats:


Then you can gently pry off the trim panel behind the rear seats:


This will allow you access to one bolt on the driver's side:


...and the bolts for both seats in the middle:


Note: You are going to have to also disconnect the airbag connector on each seat. The WIS instructions advise to disconnect the battery before starting this procedure. I did not. Even thought I did not start the engine with these airbag connectors disconnected, I did receive rear airbag malfunction messages after buttoning everything back up and starting the engine. I asked my service adviser to reset these while they are working on the vehicle.

The seat cushion parts of the seats are dead simple to remove. Flip them up and you'll be looking at all the bolts you need to remove.

In order to peel back the carpet to access anything under the seat, you need to remove the door pillar trim on each side:


And once you peel back the carpet, you will see a lot of stuff. But NO FRIGGIN' FUEL PUMP/FILTER ACCESS PORTS!