Calibrating the fuel gauge

MOGolf

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I'm posting this in 'General Maintenance' for A4s because it applies whether you've replaced the cluster or not. Those who have replaced their clusters should perform this procedure because your gauge may not be accurate (mine read high and a high reading gauge can lead to running out of fuel when you think you have fuel). If you replace the sender, your gauge may not be accurate.

Do this procedure when the gauge reads 1/4 tank or less, but not down to the red line or below.

Tools: large enough container to hold the siphoned fuel, hammer, screwdriver, Phillips (cross-head) screwdriver, siphon hose/pump, funnel, graduated container for refueling, paper towels/rags/absorbant cloths, VAG-COM or equivalent.

From right side of car:

Lift up rear seat.

Lift up carpet flap.

Place paper towels (or other 'drop cloth' material) between the sender and the door opening.

Remove 3 screws on access panel.

Lay access panel aside.

Disconnect electrical connector and move aside. I hooked it under the 'carpet'.

Push in 'button' on 1 fuel line and gently pull up to release line from sender, but do not fully remove. The 'button' is on the connector end facing away from the fuel lines.

Repeat for the other line.

Let fuel drain until you don't hear fuel draining anymore. For the heaaring impaired wait at least 30 seconds. Proceding with the retaining ring removal should be enough time.

Note position of retaining ring. Perhaps make your own alignment marks so you know when you've got it reinstalled 'just like new'.

Mark where big arrow on sender unit points to edge of opening, but don't scratch the paint. Use a felt marker, piece of tape or other appropriate means.

Take big hammer and screwdriver and whack a rib on the retaining ring to loosen. Repeat as necessary.

Unscrew retaining ring.

Stuff a paper towel around the outside of the retaining ring near the fuel lines.

Lift fuel lines off of sender and move to the side (over the paper towel).

Remove retaining ring.

Lift up sender just a bit and let fuel drain.

Repeat as necessary, tilting slightly towards the back left of vehicle.

When bottom of sender is reachable, you'll see a black part. Push up on the bottom of black part and release. Doing this repeatedly (like pushing an elevator(lift) button ) will aid in draining the fuel from the sender. You'll probably be able to see the level of fuel inside the sender.

When drained sufficiently, lift out sender being mindful of the float mechanism. Don't bend its arm.

Remove the sender from vehicle and place on a clean absorbant cloth covered surface out of the way.

You can place the fuel lines back over the opening if you want to at this point in case there is any fuel that still wants to drip out.

Siphon out fuel into a clean container. I found it useful to lightly clamp my siphon hose to the edge of the opening to keep the end of the hose at the bottom of the tank.

Pour back in 7 liters of fuel. I poured a little bit (400-700 ml) at a time into a Mason jar and poured it into the tank, keeping track of the quantity until 7 liters were in the tank.

Move fuel lines aside (if necessary), install sender unit (aligning mark and arrow) and retaining ring (tightening to the point it was before disassembly).

Connect electrical connector and fuel lines.

Do not sit in the car, but put key in starter switch, turn to power on (but don't start the car) and connect/startup VAG-COM (or equivalent).

Go to the instrument controller adaptation group 030.

If the fuel gauge needle does not settle pointing to the red mark on the gauge, adjust the number shown in VAG-COM to calibrate the gauge. A higher number increases the fuel indication; a lower number decreases the fuel indication.

When satisfied, close VAG-COM, remove the key and complete reassembly of the car. We waited until now to put the access cover back on just in case you skipped the step of reconnecting the electrical connector. This would be obvious when the gauge didn't read correctly.

Return the remaining fuel to the car's fuel tank via the normal filling orifice. This is where you may need the funnel.

Safely dispose of fuel soaked cloths.
 

mtltdi

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2003 Golf GLS, Indigo Blue
Excellent writeup! I'll do this when weather permits.
 

sodapop6620

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Lancaster, Pa
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Jetta 2000
Nice write up. I would like to suggest a couple of changes to this method. I am suggesting this way because I only had 40 miles in my reserve.


Instead of removing the pickup/sending unit just remove the fuel lines and siphon (the blue line is to the pump) the fuel out. This will give you a better idea of the empty mark of the tank and you will not have to worry about getting fuel in the car. Also if there is fuel in the tank (before being empty) and when siphoning you see air bubbles, that would indicate the o-ring in the pickup unit is leaking. Mine was and I fixed it with some fuel line attached to the pickup. Then procede with adding 7 liters or 1.9 gals of fuel and adjust the warning level.
 

AndyBees

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Great write-up!

And, as already said, I will do this one when the weather is better ...... say spring!
 

dieseldorf

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Safely dispose of fuel soaked cloths.



I like this and it sounds like a fun "rainy day" project. Ever since installing a new Rev H fuel pickup, my gage reads "high", I think. I don't hit the 1/2 mark 'til I've travelled 500 miles and then the needle friggin' plummets. I wonder if this "tweak" could correct that...
 

MOGolf

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Nice write up. I would like to suggest a couple of changes to this method. I am suggesting this way because I only had 40 miles in my reserve.


Instead of removing the pickup/sending unit just remove the fuel lines and siphon (the blue line is to the pump) the fuel out. This will give you a better idea of the empty mark of the tank and you will not have to worry about getting fuel in the car. Also if there is fuel in the tank (before being empty) and when siphoning you see air bubbles, that would indicate the o-ring in the pickup unit is leaking. Mine was and I fixed it with some fuel line attached to the pickup. Then procede with adding 7 liters or 1.9 gals of fuel and adjust the warning level.

I took out the sender because it gave me the opportunity to see what foreign objects might be lurking in there after all this time and miles. I am pleased to report that only good fuel was found. No water, no plant life, no animal life, no inanimate objects.

If you have no reason to want to inspect the inside of the tank, the suggestion of just connecting to the fuel line port is a good one and a time saver.
 

david_594

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2000 Jetta GLS Silver
I did this tonight. Come to find out my gauge was also reading a little high. One way to speed up the process if you dont have a syphon is to just run a tube from the tank into a 5 gallon diesel can. Then put the hose of a small shopvac into the can also. Use your hand to seal the can with the hose and the tube in it. This will get the tank dry REALLY fast. You can control the flow by how tightly you seal it with your hand. Just make sure you dont suck fuel into the vacuum.
 

fitzski

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Ottawa
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Uh... hmm... Well, none...
As others have mentioned, the top "half" of my tank, according to the gauge, lasts about twice as long as the bottom half. I do vent, and routinely get 150 - 200kms on the tank before the gauge even budges.

My low fuel light comes on as soon as the left edge of the needle touches the first, smaller red tick of the fuel gauge.

If I wanted my gauge to be "accurate" (i.e. an indicated half tank actually means I have half the amount of fuel of a full vented tank), could I adjust the low fuel warning point down (closer to empty) and that would effectively balance the gauge?
 

dieseldorf

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If I wanted my gauge to be "accurate" (i.e. an indicated half tank actually means I have half the amount of fuel of a full vented tank), could I adjust the low fuel warning point down (closer to empty) and that would effectively balance the gauge?

You need to decide what's "accurate" from your POV. My low fuel warning comes on when my needle is dead center over the red zone. I've been doing a little tweaking so my needle doesn't stay on FULL so long. It would hit the half way mark at 400 miles and plummet thereafter.


I think the rouinte of knowing you have 5L or 8L remaining, with the needle centered over the red zone, is a sound strategy. It's nice this setting is customizable per user!
 

fitzski

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Uh... hmm... Well, none...
That sounds like what I'd probably do... just tweak the warning point. My poor little brain has a problem trying to do the math after 1/4... 1/3... 1/2 a tank of driving and I get excited about how far *THIS* tank will take me!

Well, I guess the list of things that would justify a VAG-COM is sufficiently long, now... ;-)
 

mctdi

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se WI
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By adjusting the <font color="blue"> adaptation group 030 </font> <font color="black"> </font> is one adjusting the fuel gauge to the fuel level sending unit, or the low fuel warning lamp trip point?


Thanks,
Ben
 

weedeater

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The trip point, I believe.

The gauge is set to read 14.5 gallons or there abouts. If you vent, as I do, then the needle will say 'F' until the extra fuel is burned off.
 

vwlogue

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Reviving this old thread as I just did this tonight. Thanks for the write up MOGolf.

David_594's trick on siphoning with the shop vac is a great idea. It went quickly and there was no spill. I had to adjust the tubing up and down a few times when I got bubbles to make sure the tip was at the bottom at the tank. That's the advantage of doing from under the back seat -- you could see the bottom of the tank there.

I poured 7 liter back, and did the adaptation. I had to bump it up all the way to 136 to get the needle to get to the bottom/left edge of the red mark. Measuring group 002 read 5 liter even though I had 7 liter in there.



 

QtmMech

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vwlogue said:
That's the advantage of doing from under the back seat -- you could see the bottom of the tank there.
Is it possible to siphon MORE fuel out of the tank this way than is available to the pick up? Seems that siphoning from the fuel line in the engine compartment would give a better reading of the amount of fuel availible to burn.
 

vwlogue

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Siphoning from just before the fuel filter would get you just a little bit more. I prefer for the computer to err on the upside, not the downside. But the quickest and cleanest way is still doing it from the fillup opening with a shop vac.

Edit: the fuel gauge is linear and more accurate after the calibration. It used to show 1/2 tank after 300-400 miles of city driving, then dropped quickly in the bottom half. Now, it goes down predictably.
 
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mctdi

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se WI
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vwlogue said:
Siphoning from just before the fuel filter would get you just a little bit more. I prefer for the computer to err on the upside, not the downside. But the quickest and cleanest way is still doing it from the fillup opening with a shop vac.

Edit: the fuel gauge is linear and more accurate after the calibration. It used to show 1/2 tank after 300-400 miles of city driving, then dropped quickly in the bottom half. Now, it goes down predictably.
At what piont does your car's "LOW FUEL" light now come ON at? [ How many gal. left? ]
 

mrGutWrench

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mctdi said:
At what piont does your car's "LOW FUEL" light now come ON at? [ How many gal. left? ]
__. I haven't checked mine but on my '02 sedan, I filled up within a mile or two of the light coming on about a half a dozen times - it took consistently 14.9 gallons, leading me think that I had about 2.1 gallons (a little more than the factory spec) in that car. I've filled my '03 wagon a couple of times (passing the cheapest fuel within hundreds of miles) and took 15.3 or 15.4 a time or two.

__. So *IF* (and that's a big if) the sedan and wagon hold the same amount from dry, the wagon probably has only 1.6/.7 gallons in it when the light comes on.

__. But this isn't "scientifically tested" - it's what I hope is an "educated" guess.
 

OmegaRenegade

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was just asking about this today - glad to see theres a way to fix it - cant wait for the weather to get a little warmer! Good Write up!
 

That Guy

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Awesome thread!

I was going to clean my lines...maybe the tank...and replace my sender with the H version today, but I ran out of time. Plus I couldn't figure out how to get the lines off of the sender>>>>which led me to this thread tonight.

I may try that shop vac trick when i do this tomorrow....and the calibration too, which i didn't know could be done. :)
 

silverbox

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Great thread, I just re-calibrated my fuel gauge. It's nice to have some reserve again.

P.S. I did not empty the tank; On my last fill up, when the warning light came on, I pumped in 61 liters vented and seeing the fuel at the top. This seemed a little too close to empty for me. Today through VCDS, I lowered the needle to the red warning hash. On the way to the fuel station(1.5km) my red light came on , I filled up until saw the fuel in the neck, with 57.4 L. I know this is not the most scientific way to do this but it's very clean.
 
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Steamroller69

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My problem is that even the fuel is overflowing out of the neck, my guage still doesnt read full. I may try to adjust it up 1 uning vagcom at each fill up until it reaches full. I guess i am risking running the tank empty but i know what it holds so when it reaches the red i can fill it and count backwards to figure how much was remaining
 

BobnOH

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central Ohio
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My problem is that even the fuel is overflowing out of the neck, my guage still doesnt read full. I may try to adjust it up 1 uning vagcom at each fill up until it reaches full. I guess i am risking running the tank empty but i know what it holds so when it reaches the red i can fill it and count backwards to figure how much was remaining
Try cleaning the rheostat bit on the fuel pump in the tank.
 
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