On my 240D when you turn the ignition switch on the low fuel light in dash triangle lights up. I was getting down to where the fuel gauge needle was near the E bar, and the low fuel triangle light wasn't on yet. Is there a way to test it, if it works, while still in the tank? I was queezy about going much further, on account of, running out of fuel.

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Rebe

Its easy to test, just pop the connector apart that plugs into the sender...touch the wires together...one wire will light the light, other will peg the gauge. The light is suppose to light before the car starts...well early years they don't. The light won't come on till the float hits the bottom of the sender, it will then come on notifying you, that you have 3 gals left. It is very very likely your sender needs to be pulled and cleaned also.

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If the contacts in the Low Fuel part of the sender are dirty from years of use the light may not work. Remove the sender and clean the contacts.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Or don't let your fuel tank get that darn low in the first place!

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2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)

That is way way to easy of a fix

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The bulb self test for the low fuel light came in on the later 123 gauges.

I wrote a post on this thread about how to clean and test the sender

w123 out of diesel at 1/8 tank

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Problem with the gauge is the build up of gunk in the bottom of the sending unit. Remove the Sender and clean it will usually solve the problem.

I use a 46mm or 1 13/16" Socket I cut in 1/2, the filled the 3/4" drive hole with an old 3/8" socket we cut down and welded in the hole. Tis way I don1t have to use several reducers to use a 3/8 Ratchet. there isn`t a lot of room between the back glass and the Sender. this Socket can also be used for the Tank Screen on the bottom of the tank.

Here is a good thread on the subject.
W123 300D Fuel tank sender question


This is for a W124 but the same as the W123 as far as the insides go.
DIY w/pix -- W124 fuel sender disassembly/cleaning/testing

Fuel Sender 85 300D- Cleaned (Pics)

Fuel Gauge and Sending Unit threads

https://www.flickr.com/photos/sfgabe/sets/72157600616798587/



Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Its not always gunk, sometimes the very thin wire inside the sender breaks free. I had to take mine out, clean it, open it, resolder the hair-thin wire Not an easy task, as a warning, I am experienced with soldering and it was still a pain. When I put it back in, all good, light came on when starting car and when fuel is low.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

You are right, that can happen also.

W123 300D Fuel tank sender question


Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I remember removing one of the units quite a few years ago. Cannot remember the delemna for taking it out anymore, but I do very much remember the fragile tiny little wires. I guess, I will pull it out of the tank, and do the right side up out of tank, and the upside down test to see what the outcome is. Even though it works, it would probably merit a maintenance cleaning. Although the light is probably not a necessity, they can give you a wake up reminder. It's not always pleasant getting cranked up and running again on one of these diesels, after running out of fuel.

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Rebe