Got the SRS light on in my 2004 E320 and accompanying message on center display. Did some researching and found out it's related to the passenger seat mat sensor. Dug in last night and went to work. Here's my procedures. Sorry no pictures, but it could help someone since the only references I had to work with were

this person's for the seat removal

https://mbworld.org/forums/w211-amg/...-2006-e55.html

and this person's for the sensor replacement and it's for a W210 (which is different and I'll explain that now). BTW, my passenger seat has memory and power, but no heat or massage feature.

http://www.benzworld.org/forums/w210...placement.html

Seat Removal

1. Move seat all the way back. Remove 2 E bolts with an E12 socket.
2. Move seat forward. Remove 2 E bolts in back
3. Move seat to middle and lift to highest point to give you the best access.
4. Disconnect aux battery located under cabin air filter passenger side engine bay. This is to avoid any other SRS fault lights that could go on.
5. Unplug the three connectors located under the seat. The yellow connector in particular contains the plug for the SRS seat mat sensor.
6. Remove cover for seat belt. Remove torx bolt holding seatbelt to seat.
7. tilt seat forward, open passenger door fully and slide seat out.

SRS Seat Mat sensor removal - I definitely recommend placing the seat on a workbench as the work can be grueling on the shop floor. This work can be done by one person.

1. Remove the plastic panel located to the right seat base which is held in place with a torx bolt and two 10mm bolts.
2. Remove the left side smaller plastic panel which is held in place by two 10mm bolts
3. Tricky part - The center front of the seat base has a convenience storage door (easily removed) held in place with a metal bracket. This metal bracket will make removing the front part of the seat cover impossible. In my case, I was able to bend the front of the bracket such that I had just enough room to remove the seating material. This metal bracket will get in the way and is held in place by pop rivets. The proper procedure is likely to snap the pop rivets and remove the bracket.
4. Once these ancillary steps are completed on to the actual seat base removal. Under the seat base on the left and right side are 4 metal upholstery clips that hold the seat leather down. Using your hand, pry the cloth/leather material away from the clips.
5. The front of the seat base is simply held to the metal base by a plastic border. Gently pry that up and you're done with this step.
6. Located under the seat leather/cover are metal bars that are held by fabric sewed to the leather. The bars are held against the seat foam with plastic hooks. You can use a screwdriver to remove the bars from the hooks, but use caution.
7. There will be 3 lateral metal bars held by 3 hooks each and 3 horizontal metal bars each held by 2 hooks. This is what I considered to be the toughest part of this job. There's no easy way to remove these and to avoid damage, you should simply use your bare hands, no tools if you can help it.
8. Once you've done this, you've accomplished the toughest part of this job. The seat cover will pull away from the foam, revealing the seat mat sensor. I ran continuity tests on my sensor and it was in fact bad.
9. Remove, replace faulty sensor with new one. Quoted $318 for the sensor (no discount) from my local stealership. This is definitely not something I could find at a retail auto parts store.
10. Reverse steps to install

Note - It is not necessary to remove the entire seat base assembly from the metal frame of the seat as described in the W210 procedure.

I did not have to get the SRS light reset by a tech or STAR diagnosis. Once I started car, airbag light went on, then off.

Good luck.

 

Thanks for the writeup. You can get good discount and OEM parts from parts.com