[V8] Audi V8 speedometer

urq urq at pacbell.net
Thu Jul 16 17:28:55 PDT 2009

If you have a service manual for the car, check it to find out what the
resistance readings are supposed to be for empty and a full tank.  Over the
years there have been several possible culprits for this sort of problem,
from instrument voltage regulators to sending units to the gauges
themselves.  In the old days you could check everything outside the sender
with a programmable resistor you installed in place of the fuel sender.  Set
the resistor to the "full" resistance and the gauge better read full.  If
everything worked with the programmable resistor you knew the problem was
the sending unit.  

If the 100CS is new enough to have the OBDII installed you should be able to
run diagnostics on the IC which can help troubleshoot the fuel gauge via the
OBDII interface connector using VAGCOM or ProDiag (I keep forgetting the new
name).  Chances are the diagnostic will be able to set particular fuel
levels which you can confirm visually.  The V8's cluster has similar
diagnostics, but they are accessed via blink codes.  

Steve Buchholz

-----Original Message-----

Next complaint that I have is with my wife's 100CS fuel gauge that reads
terribly pessimistic.  I suspect that it is a ground. The cluster in that
car was out last winter and had all new bulbs installed, so I am reluctant
to mess with it again for the time being, but I am sure there are
explanations out there for why the fuel gauge reads empty when there are
still seven or eight gallons remaining.  I don't care, but it make my wife
nervous.  And as I am sure, when the wife is nervous, we are ALL nervous!


More information about the V8 mailing list