It would seem the multimeter is functioning correctly if you have infinite resistance when the leads are not touched together and zero resistance when they are touched together. When you use the multimeter, be sure there is no power in the circuit or you will obtain a false reading or damage the multimeter.

There are several on line retailers for Audi OEM parts that are Audi agencies and sell at a discount. You may want to search on the Internet for one near your location.

Here is a link to the publisher:
Bentley Publishers - Repair Manuals and Automotive Books

 

Thank you so much HBAudi for all of the help. I'll post once I've bought and installed a new sending unit. Hopefully that'll fix it!

 

Time to reboot this thread. I ordered a new fuel level sending unit, and it arrived today. First thing I did was check the ohm readings to see if they were the same or different from my other units. To my disappointment, they were identical. But, I decided to try out the new unit anyway. I plugged it in, but left the sending unit hanging out of the fuel tank. I figured that way I can adjust it by hand, and see if my fuel gauge responded accordingly. To my dismay, my fuel gauge still read a little over the 3/4 mark when I moved the sending unit to the "full" position.

Now, perhaps this will save me the $180 plus taxes for the sending unit, but now I have to continue this mission to figure out what the problem is... I'm about to head out with a toothbrush to see if it's any of the connections, though TBH I doubt it...

Any chance it could be the ECU reading incorrectly? I just bought a GIAC chipped ecu from the classifieds section, so once it gets in I'll be able to see if that fixes it, but in the meanwhile, any suggestions?

 

That is very disappointing that the new sending unit behaves the same way. Before spending any additional money, check all the connections and any earth (ground?) points you can find.

It is possible that the ECU could be having a problem, but this is also an expensive guess. Start with checking the obvious and eliminating all those possibilities first.

 

Ok, I forgot that I had an extra ECU hanging around that I had pulled out of a junker a while back. I tried that, and it didn't change anything. (It was a M instead of CH, but I changed the software using VAG just to make sure, and that still didn't do anything.)

I also tried cleaning the connections, even though they all look very clean. Still no luck.

I guess I'll start hunting for some ground (earth) connections, but tbh I'm not sure where to start. I guess there's a couple obvious ones in the engine compartment, but are there any closer to the fuel tank that may be connected to the body under the car, or worse yet; under the upholstery inside the car?

 

There are some under the back seat as well, not too hard to pull up the back seat...I'll see if I can find the diagrams for the grounds for you.

This may help you out with the grounds...

 

I check the one on top of the engine, the 2 that are under the dash (above and to the left of the pedal cluster), and tried to find the one that's in the trunk unsuccessfully. I looked under the rear seat and didn't see any ground connections.

 

I have a ground connections schematic in my B5 shop manual, it is, however, 1.5MB, so can't upload it....it lists with wiring diagram all the grounds in the car...

 

There's a ground strap that goes from the fuel filler neck to the chassis, it's a strap...see pics...

 

So just to recap, after putting in the new fuel sender is the only problem you are experiencing with the cluster is just above 3/4 tank reading or does it still move to empty after 125km? When the cluster is powered down, where does the needle sit for the fuel gauge?

Doug