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Discussion Starter · #1 ·
hello everyone,

i have a 2001 TT quattro 5-speed that has fuel gauge issues. i have removed both sending units and cleaned the contacts but that didnt solve the problem. if i measure resistance across pins 2 and 3 of the fuel pump housing, i get 150 ohms which indicates the sending units are measuring fine. i measured the wire that goes from the gauge cluster to the sending unit, and that ohmed out to less than 5 ohms, so i can safely assume there are no breaks in the wire. VCDS measuring blocks show 0 ohms and a code of 00771 29-00 short to ground. i took the gauges out and wired them up for a bench test. checked for power at pin 5 and measured 0 volts to ground, but i get 5 volts if i measure pin 8 to ground for coolant gauge. is it safe to assume that i should be seeing 5 volts out from pin 5 as well?
 

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Looking at the EWD in the Bentley to try and work through your thinking.
T32/5 runs to pin 3 on the fuel level sender then to ground. T32/8 runs directly to the ECT sensor then to ground. So your thinking is that because the ECT signal wire has power then the FLS signal wire should also have power.

Except the fuel level gauge also shows a connection to A27 (vehicle speed signal) and J220(ECM pin 54) via pin T32/3. T32/3 also feeds K14 (parking brake warning light) which is grounded through a mechanical switch on T32a/13.

T32 is the blue connector
T32a is the green connector

If I understand this correctly, iff there's good signal on T32/3, I would expect grounding T32a/13 would turn on the parking brake light. Iff there's good signal on T32/3, then a potentiometer inline to the ground on T32/5 should let you operate your fuel gauge.

Then again, I'm a math turned compsci turned datascience nerd. I'm no eletrickan.
 

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Discussion Starter · #3 ·
would you be able to post a photo of the schematic you are following? the only one i have been able to find online that i can access for free is from a 2006 (but they should be the same from 1998-2006). i think maybe you mis-interpreted my thinking as far as the ECT and FLS signals having power. i was trying to set up a bench test so i could move the ECT and fuel gauges via a potentiometer. to do so, i hooked the potentiometer to T32/8 and ran the other leg to ground to complete the circuit. when doing this, i was able to turn the pot and watch the gauge move. i tried this same principle for the fuel gauge by hooking the pot up to T32/5 and the other leg to ground and i cannot control the gauge. my assumption was that for any sensor in the car to operate, it needs to power the sensors with a 5v reference source. i am getting between 3.5-5v from T32/8 when measured to ground, but i am getting 0 volts when measuring from T32/5 to ground. im not entirely sure what T32/3 has anything to do with when it comes to the FLS or ECT because on my diagram, T32/3 does not go to either of these gauges.
 

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Discussion Starter · #4 ·
i got the gauge working. it appears there was a cracked solder joint on the board. i discovered it when tracing the bus-line back for T32/5. above the tach on the edge of the board are 2 resistors that get the same power from 1 location. both had 12v going in but only 1 had 4.5v going out. i touched the solder joints on all 4 spots of the chips and now i get 4.5v to pins 5 and 8 on T32. now i just need to replace the LCD and i can reassemble.
 

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Awesome. Glad you found the break.
As for the diagram I'm using. It's EWD-18 No. 1/7 in the Bentley manual.

Rectangle Slope Font Parallel Pattern

Font Circle Rectangle Number Magenta


Can't say I know of any good free sources.

Only bad thing I have to say about the Bentley is they decommissioned the phone home endpoint for eBahn software activation. Most everything is in the book, but there's still some detail in the software that made it a valuable add-on.

I think you can get the same level of detail with an erWin subscription. I've not had a need to fully check that out. The A3 is still dealer maintained and the TT is sorted.
 
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