Poll - Failed Fuel Sending Unit(s)
AudiWorld Super User
Joined: Apr 2002
Posts: 3,384
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They corrode, possibly due to oxygenated gas. If you take it out...
you can use a pink pearl eraser to burnish the contacts, and they will be back to normal. I had to do that once, about 30K ago, been fine since. I expect I'll have to do it again at some point.
(corrode, not like getting eaten away, but like develop an insulating oxide film)
Here's a post I made OTOF at the time:
My fuel gauge was reading high - close to 1/2 with over 300 miles on the trip odometer, a natural event on a TDI, but not on a TT.
VAG-Com showed the resistance fluctuating (measuring block 2), so I pulled the fuel pump. Attached to the side is a ceramic circuit board with multiple contacts and resistors across which a set of sliding contacts move with the float. I figured that corroded or contaminated contacts were the problem.
To get to the contacts, you need to remove the metal rod which holds the float. It's a press fit and can be removed by carefully prying with a small screwdriver. After doing so, the plastic piece which holds the moving contacts can be removed easily. The circuit board is on a plastic carrier, after removing it, the circuit board can also be removed.
I then cleaned both with a contact cleaner, then used a "pink pearl" eraser to lightly burnish all points of electrical contact.
Put it back together, and not much change at all. Foo. But, I've got a Quatto, so there's a second sender in the left side of the tank. The two senders are connected in series so the gauge reads the sum of both sides of the tank.
Pulled the secondary fuel pump, and cleaned those contacts, too. That took care of the problem - the gauge now reads about 3/16, where it read 7/16 before.
Much cheaper than a new right side sender (about $80) or a secondary pump (about $135, no separate sender available).
(corrode, not like getting eaten away, but like develop an insulating oxide film)
Here's a post I made OTOF at the time:
My fuel gauge was reading high - close to 1/2 with over 300 miles on the trip odometer, a natural event on a TDI, but not on a TT.
VAG-Com showed the resistance fluctuating (measuring block 2), so I pulled the fuel pump. Attached to the side is a ceramic circuit board with multiple contacts and resistors across which a set of sliding contacts move with the float. I figured that corroded or contaminated contacts were the problem.
To get to the contacts, you need to remove the metal rod which holds the float. It's a press fit and can be removed by carefully prying with a small screwdriver. After doing so, the plastic piece which holds the moving contacts can be removed easily. The circuit board is on a plastic carrier, after removing it, the circuit board can also be removed.
I then cleaned both with a contact cleaner, then used a "pink pearl" eraser to lightly burnish all points of electrical contact.
Put it back together, and not much change at all. Foo. But, I've got a Quatto, so there's a second sender in the left side of the tank. The two senders are connected in series so the gauge reads the sum of both sides of the tank.
Pulled the secondary fuel pump, and cleaned those contacts, too. That took care of the problem - the gauge now reads about 3/16, where it read 7/16 before.
Much cheaper than a new right side sender (about $80) or a secondary pump (about $135, no separate sender available).
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