# fuel level sensor question



## whitey_b (Oct 8, 2008)

Using the info on audiworld I removed the rear seats of my car today and got out my multimeter...unfortunately I couldn't get any readings from it (user error).

Anyway, with both sensors unhooked I had no readings from the fuel guage. With the right (passenger) side hooked up but the left (driver) side unhooked I had no readings. When I hooked up the left side the gas guage jumped up.

Would this indicate the passenger side sensor is bad or do I need to figure out the multimeter to be sure?

Also...where is the best place to purchase sensors? Neither ECS or BP carry the sensors.

Thanks.


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## monkeytronic (Oct 5, 2009)

You didn't mention any specifics re: the car in question but its worth noting that US market gasoline powered FWD C5s only have one fuel level sender while AWD C5s have three fuel level senders.

Therefore, I'm assuming you've got either a V6 or V8 C5 quattro and the third fuel level sender is located at the center rear of the fuel tank under the trunk floor right behind the rear seat backrest. Pull the trunk carpet to get at its access cover.

The resistance of all three fuel level senders gets summed together which means that all three level senders must be connected to each other to get a reading at the fuel pump connector. The rear sender is wired externally to the front driver side sender via wiring that runs along the front rollover valve vent line which is wired internally to front passenger side sender at the fuel pump via wiring that runs inside the tank along the suction jet pump's fuel lines.


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## whitey_b (Oct 8, 2008)

I'm sorry...I violated the cardinal rule...yes, the car is a '98 2.8l 30v A6 Quattro. Didn't realize there was a third sender.

Are you saying that I cannot measure the resistance at each sender to determine which one is faulty?


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## monkeytronic (Oct 5, 2009)

You can measure the resistance of each sender separately just as long as all three senders are disconnected from each other.

With all three senders connected together, you should see approx. 70 ohms empty and 270 ohms full when probing the middle two pins of the fuel pump connector.

Since you've got a '98, it's worth noting that Audi changed the sender resistance ranges around February 1999 which may or may not be an issue depending on the exact build date of your car.

That said, after disconnecting all three senders, probing each sender independently you should see...
Front passenger side level sender: approx. 10 ohms empty (20 ohms empty when installed in the tank) and 70 ohms full
Front driver side level sender: approx. 20 ohms empty and 118.5 ohms full (108.5 ohms full after 2/99)
Rear level sender: approx. 30 ohms empty and 81.5 ohms full (91.5 ohms full after 2/99)

BTW either the front driver or passenger side fuel level sender has to be removed from the tank to disconnect it from the other front fuel level sender to test it because both senders are wired together inside the tank. Make sure the tank's fuel level is below 1/4 tank before attempting to remove either sender.


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## whitey_b (Oct 8, 2008)

Thank you very much! The diy on audiworld was not that detailed. 

Thanks!!


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