After having no Mercedes for about 1.5 years, I'm back in the MBZ S-Class club. Went with a W140 S420 this time.

 

Hello All!


Not quite sure how to post on this forum as a new member, but I have an issue with a W140 that I'm hoping an expert here might help me with.


First, I have a 1993 300SD turbodiesel with 242K miles.


Among the many issues I'm working through, the one most bothersome is the inop fuel gauge. Regardless of how much fuel is in the tank, the gauge always reads zero and has the low fuel warning light on.


I took the sender out of the tank, carefully cleaned (it wasn't too dirty), reassembled, and it ohm checked good. Next, I put the cluster in diagnostic mode and the fuel quantity indicated zero, as I expected, and then when I cycled through the overrides it hit the lowest mark, then 1/4, then 1/2 and full. I thought that was a little strange as the overrides are supposed to go 1/4, 1/2, 3/4 and then 1/1.


After removing the cluster and finding nothing obvious, I'm down to two possibilities. Or at least with my very little Mercedes knowledge, what I think could be two possibilities.


First, it could be the gauge. But why would the needle move in Dx mode? Next, I'm thinking it could be the wiring to the sending unit, but in order to check that, I need to know which pin(s) go to that component.


Rather than start pulling things apart, I thought I would check this forum to see if someone has a pin out diagram and maybe some advice that would be helpful as well.


Thanks for starting this thread. I hope my post is in line with how you all conduct business here.


Thanks in advance for any replies.


Jim