One day I was sitting in my car and I noticed the fuel gauge
oscillating back and forth. Shortly after that, it started telling me that I was
out of gas, or much lower that it should have been. I read on Rob's Audi World that it
is a common problem for a wire to become frayed or broken and interfere with the
proper operation of the float bar on the fuel gauge sending unit.
decided to dive in and try to fix it myself. Here are some pictures I took and
advice I have to give. Do this outside on a sunny day so the gas fumes do not
build up and the sun will quickly vaporize the evidence of your chemical spills.
Also, gasoline vapors are heavier than air, so keep your head high and you'll
avoid most of the fumes. Finally, please read the entire procedure before
attempting this repair.
Fuel vapors are flammable. Exercise extreme caution when working on or
near the fuel system. Sparks, open flames, smoking and other sources of
ignition could ignite fuel vapors and cause an explosion. Always use a
flashlight when working near the fuel system--if a drop light bulb should
happen to break the bulb element could ignite fuel vapors.
Remove the three philips screws in
the fuel door. This is located in your trunk under the carpet next to the spare
The area under
this door is exposed to the outside world and will be very very dirty. Well,
that is until you spray gasoline everywhere, but that comes later. The first
step is to remove the electrical cable connection. This provides power to the
pump and pins 2 and 3 are connected to the sending unit. Next remove the crappy
Audi hose clamps on both hoses. You should buy some 5/8" screw type clamps to
replace them with as they are not worth trying to save. The hose with blue
lettering is the fuel return hose. Remove it first. Expect the hose to put up
one hell of a fight. I just grabbed and twisted the metal part of the hose with
my pliers to work it loose. A few drops of gasoline may leak out of here. The
hose with white lettering is the fuel pump outlet. This hose is pressurized even
when the system is off. Because of this simple fact, the hose will shoot off the
nipple with only the slightest tug, squirting roughly 2 cups of gasoline
everywhere. You can try to plug it with something, but that won't help you when
it's time to put it back on. I tried to catch it in my gas can, but gasoline
doesn't flow uphill and the hose is too short to get it above almost any
container. Any liquids spilled into the access door opening will drain out on
the ground. Clean up your mess and remove as much dirt as you can.
(Editor comment: remember, avoid sparks. Use a brass drift, non-ferrous
metal or wood for safety)
The large black plastic
ring you can see in the above picture needs to be unscrewed. It is on incredibly
tightly. You can get it off using an enormous pipe wrench, or you can use a
great big flat blade screwdriver and a 3 pound sledgehammer to turn the nut
loose. BTW: loosen is counter clock wise. BTW2: Did I mention this thing is
tight? Don't get any ideas about tapping your screwdriver with a pair of pliers.
This nut is FREAKIN' TIGHT! You will need to hammer the crap out of it until it
breaks loose, and maybe even a lot more after that. While you are here, make
note of the arrow on the white porthole plug. Make a small mark on the metal it
points at to aid alignment during reinstallation. Lift the port hole cover. This
is what you should see:
careful not to drop anything in there that could contaminate your
On the base of the sending unit, there is a large black
plastic button. You must push this button in order to remove the sender and
float assembly. I did this when my gas tank was almost completely empty (which
can be hard to do if the gauge is malfunctioning.) If you tank is not empty,
some or all of what you see here may be submerged in gasoline. Consider
siphoning most of your gasoline out. Gasoline will dry your skin out pretty bad,
but on the grand scale of things, it's really not all that bad for you
externally. Just make sure you wash thoroughly before rubbing your eyes, picking
your nose, or eating your boogers. You might also want to apply some lotion
afterwards. A bright compact flashlight like my Streamlight
Stinger can make your life much easier. Those wussy LED flashlights aren't
even in the same league as this baby. Lift the sender out being careful not to
bang the float on anything.
On the bottom of the white
porthole plug are two electrical connectors. The white one goes to the fuel
pump, and the black one goes to the sending unit. Unplug the black one.
This is the sending unit. The wire
marked is known to fray and break, and thus needing replacement. You can
unsolder it at both ends and replace it with a 26-30 gauge teflon insulated
wire. However, as you can see, mine is just fine. Also, there is no need to run
it under the bail as shown above. I have no idea what possessed some engineer at
Audi to do that.
time to read the directions. The shop manual says that the sending unit is just
a variable resistor that should read 280 ohms at empty and 40 ohms at full. When
I tried to measure it I found the copper terminals in the connector were black.
Ack! My meter really had a hard time getting a stable reading. I scraped a
little off with my fingernail, and then it read perfectly. So it needed cleaning
eh? I went after it with an old toothbrush, but that really didn't make a dent
in it. So I put a little baking soda toothpaste on the brush and went to town.
Now it looks like this. The poor contact is the reason why my fuel gauge was
often reading low or unstable.
When putting the system back together,
make sure that the sender is completely free of water or dirt, and follow the
directions above in reverse. Since it is just a resistor, it does not matter
which way the plug goes back on. If you are having trouble getting the sending
unit back in it's proper place, look below for this socket on the rear of the
fuel pump. Push it down firmly until it snaps in place.
Make extra certain that you tighten
the big black ring super tightly. Its important to get a good seal or gas vapors
might leak out. Expect to do more hammering again. When it's fully seated, it
will sit tightly against the white plastic porthole cover. If you can slip
anything under the nut, it's not tight. Also, it's very easy to cross thread the
nut. To avoid this, turn it CCW, pushing down gently, until the threads drop
into proper alignment. Then tighten clockwise.