I have a 1990 Audi 100 2,3E with speedo problems that have been
bugging me for some time. It started last summer when the speedo
needle during drives from time to time stuck at about 80 km/h. It
would then after some minutes usually fall to 0 km/h where it also
could stick for some minutes until is went back to indicating the
speed in a normal fashion. In outbursts of aggression and brute force
it has been tried to knock on the top of the padding covering the
instruments with an increasing amount of voilence. Some times this
actually seemed to work because the speedo needle suddenly started
indicating the correct speed again, but I don't know if the hammering
incidents actually have caused the speedo to start working. After some
months these problems seemed to occur more frequently and a couple of
months ago I got the entire panel with instruments changed to a brand
new one from an Audi dealer. The cable connections also got checked
and were said to be fine. Some minor components also were changed at
the same time.
Now the problems seemed to have reoccured with the speedo needle often
sticking at 78 km/h then fast falling in a number of steps to 0 km/h
and often rising again to indicate the correct speed or sticking at 0
km/h for some time before getting functional again. Right now the
needle is stuck at 78 km/h and has been for a period of time.
The driving speeds have been almost all over the entire range from 0
to 200 km/h when the problems have occured. Moreover the counters
indicating the distance covered for the car also don't work when the
speedo needle gets stuck at either 0 or 78 km/h.
Any good advice on these problems?
As you are aware the speedo in your car has electronic input to the
display. If the problem was not corrected by changing the cluster you
should check the wiring leading to the speed sensor which is located on
the trans axle (behind the engine). I think it is on the left side
(driver's side in the US).
I think that the circuit runs to the ECU and then to the IC so checking
the connections to the ECU would be another place to try. Unplug the ECU
and plug it in again to check for bad contacts. The ECU is located in
the right side kick panel, just in front of the door. There is a
possibility that the engine electronics also is controlled by a module
in the left side kick panel. These have been known to get corroded
connectors due to water leaking from the sun roof. They have a plastic
protector to help keep them dry but moisture still gets in over time.
I have now checked the wiring and connections for bad contact and
corrosion and I found nothing. All seems fine except the speedo is
still not working properly. Right now the only thing I can think of is
if this could be a fault internally in the ECU? I would prefer not to
have to buy a new ECU (I just heard the price from a Audi dealer), so
can I swap the ECU with the ECU of another Audi? And if so, from which
models is it possible to find a usable ECU?
Alternately I could also have a go at looking for a diagnosis on the
actual ECU if I can find the time for it. I have access to electronic
lab equipment at my university, so in this case I would like to know
where to find a description on how the ECU should perform under normal
You would need to find an ECU from the same model. Check the Audi pert
number on it to verify. OTOH, it is unlikely that the ECU is the
problem. They tend to be almost bullet proof.
Try checking this site:
Or this one:
AudiWorld forum for T44s would be worth a check too:
I would try to check the output of the speed sensor before doing
anything else. This might require a scope but a multimeter might be enough.
I checked with a friend that is an independent Audi mechanic and he said
that on the '91 T44 the speed signal does not go through the ECU. It is
a direct connection from the speed sensor on the right side of the
transmission to the instrument cluster.
His opinion is that the sender or its wiring is the problem. The part is
cheap at about $30US and easy to replace.
Let us know what you find.
If the Audi dealer changed the instrument panel for a brand new one only a
couple of months ago, haven't they given you a warranty on the work?
Not sure of the consumer laws in your country but if the dealer said that
replacing the panel would fix the problem and it hasn't then they haven't
done their job properly and should rectify it with no charge to you.
Oh yes, there is a general warranty on such work in Denmark. But I
also remember the guy putting it someway like 'We'll have at go at
solving your problem by replacing the instrument panel'. And I do
understand that attitude because it seems most likely to eliminate
this sort of problem by doing that - also from the advice I recieved
here. And I seriously expect that the next steps in eliminating
further possible causes to the problem is selling me more expensive
The slam on the binnacle is known as the "eyebrow dashboard salute".
This is a known problem caused by a pin soldered into the backplane
that's used to support the speedo cracking the solder that holds it to
The fix is a tiny touch with a soldering iron and it's documented on
Scott Mockry's site at http://www.sjmautotechnik.com
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