Fuel Gauge on 2003 ML350

It is a strange problem. When I fill the tank completely the gauge reads empty but I don't get a low fuel light. Once about an eighth of the tank is used the needle jumps and gives a proper indication.
Obviously its malfunctioning. Is this a common problem?
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The sender in the tank has malfunctioned. There are two sensors in the sender. One is a sliding contact on a shaft that runs against resistance wire. The more current that goes to the gauge, the more fuel is shown on your gauge in the cabin of the vehicle. Your resistance wire has broken, so the sender is sending no electricity to gauge when the fuel level raises the sensor above the break in the wire.
The "low fuel" warning light operates more simply. The same float that moves the other sensor along the coil of resistance wire also has a fixed contact sticking out from it and when the sensor drops to a low level, that contact meets another low on the shaft and completes the circuit, turning on the low fuel light.
So, in general, you can trust the low fuel light, and probably also the gauge once it starts to register.
You can remove the sender and try and replace the resistance wire if you can find any anyplace. I fixed the sender on my 1982 300 TDT, but it was really hard to get the resistance wire because nobody sells it retail and the wholesalers sell it in 100 meter lengths that cost more than a new sender. I finally just hit on a guy at a wholesale place I found by doing a Google search for resistance wire who sent me 34 meters of wire for free.
To find out what size of wire you need you have to remove the old wire and then use an ohmmeter and metric measuring device to calculate the ohms of resistance per millimeter. You can use Imperial units if you like, but you will get only close then and your gauge may slightly vary from the factory operation. Resistance per length of wire is the important parameter.
If that sounds impossible then you should get a new sender.
Resistance wire available here: http://www.bobmartinco.com/reswire.htm
http://www.installuniversity.com/mb/w203/w203/fp.html
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Nice and informative post. I bet a lot of us learned from this post!

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Depending on where you live... and when you noticed this happened... gas station dirty fuel will kill the fuel gauge along with engine trouble. If the car is still under warranty, get it fixed.
If not, you still need to have the fuel sender changed out.
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Tiger wrote:

If the car isn't under warranty how much will it cost? Guestimate.
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You should contact Mercedes dealer on this matter... It is extremely unusual for fuel tank sender to die in 5 years. Maybe they will repair it for free or nominal cost. You should contact MB USA headquarter on this matter if dealer won't help.
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Tiger wrote:

I highly doubt they'll fix it for free since its out of warranty. As for the dirty fuel, I find that unlikely. I always put premium in, and I never go to discount gas stations like Coastal, Giant or Redner's. Anyway thanks for the info next service I'll have it fixed.
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I had bad gas (too much sulpher) from Chevron in my 1999 C280 and chevron ended up pay close to $2000 for new fuel senders and an instrument cluster. This happened in 2004. The cluster was needed because the new updated senders wouldn't work with old cluster.
Jojo

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