Fuel Gauge or Sensor? - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 08-08-2013, 08:24 AM Thread Starter
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Fuel Gauge or Sensor?

Does anyone know the proper resistance for a W115 fuel level sending unit?
My fuel instrument gauge is stuck on 'F', so I pulled the unit out of the fuel tank. It wasn't horrible dirty and the float is working fine. I have a resistance of 9 ohms when it is up and 70 ohms when it is down. If I remember my physics, V=IR, so I should be getting current differences of 1A down to 0.12A.
So I'm thinking it's the gauge...
And the copper wire in the sending unit to operate the low fuel indicator has corroded off , but I can fix that...
Thanks, Bob
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post #2 of 6 (permalink) Old 08-08-2013, 09:36 AM Thread Starter
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I've answered my own question by hooking up various resistors across the leads of the sending unit. The gauge registered half-full at 1000 ohms, so I have a short in the sending unit, and the gauge is fine.
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post #3 of 6 (permalink) Old 08-08-2013, 10:23 AM
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Originally Posted by Cheetahpop View Post
I've answered my own question by hooking up various resistors across the leads of the sending unit. The gauge registered half-full at 1000 ohms, so I have a short in the sending unit, and the gauge is fine.
If you come up with a fix for this please share it with me. I have having the same issue and was wondering if I can repair the sendor/sensor or if I need to find another.
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post #4 of 6 (permalink) Old 08-08-2013, 04:10 PM
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if you unplug the sending unit in tank , the gauge in dash will go to empty .
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post #5 of 6 (permalink) Old 08-08-2013, 04:42 PM
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Senders can be cleaned but you've got to be gentle. The thin wires snap easily. The senders aren't that expensive and are available. Replace the gasket at the same time no matter how good you think the old one looks.
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post #6 of 6 (permalink) Old 08-10-2013, 09:39 AM Thread Starter
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The copper wire for the "empty" warning light had corroded off, and I discovered that the wires for the gauge are coated with something to increase the electrical resistance. So, apparently, that corroded off the other wires as well.
I ordered a new one...
Thanks, guys.
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