Fuel Level Sending Unit Resistance W123 240D - PeachParts Mercedes-Benz Forum

Rafi · #1 03-27-2009, 01:17 PM

My fuel guage was stuck at full all the time, I did not know if the guage was faulty, or there was a short to ground, or the sending unit was stuck with the float all the way up. This is a 1982 240D W123. I removed the First aid kit housing and removed the sending unit connector, easy enough, and the guage goes to E, great it is the sending unit, easier to get to than removing the instrument panel or finding the short to ground somewhere.

I removed the sending unit, I had 46 mm socket (based on reading this forum). I took apart the sending unit by removing the nut on the bottom of the sending unit by using C-ring pliers. There was a lot of gunk like everyone else experienced. I cleaned it really good with carb cleaner and put the unit back together. I measured resistance between 1 and G pins. There are 3 pins 1, G, and W. 1 goes to ground G goes to guage and W is for the reserve light. I measured ~ 2 ohm between pins 1 and G with float at top and ~58 ohm with float all the way to the bottom but the guage reads 1/4 tank and the reserve light is on, good the switch also works.

I suspect the prevous owner replaced it with the wrong part for this car, because the float is all the way down and if it was not making good contact on the wire inside the unit the resistance would be higher, so that is not the case. The part I was working on had number 123 542 0604. Phil has two part numbers for this car depending on the S/N range.

Part numbers
W0133-1599001 which is 123 542 0604 resistance range 2 - 58 Ohm
W0133-1604571 ??? ???

Does anyone have resistance reading on the second part number ? I suspect it should be 2 to about 77 ohms based on {([58-2]/0.75)+2}

WD8CDH · #2 03-27-2009, 03:27 PM

I don't know the part number but several that I measured were around 78 ohms. (my two 300Ds and the 240D)