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Discussion Starter #1
OK folks. Now that I have my beast back in running order and cruising the streets I have another 'niggle'. The speedo has a mind of its own :w00t: It doesn't seem to show the correct speed. At present its sat on the drive doing 30mph :grin: If you accelerate fast the needle travels up very slowly until 50mph where it stops. I can be in a queue at walking pace but the speedo shows 40. The it drops down to 0 and stays there.
I know there is a sensor on the gearbox but can you check if it is that with changing it for another.
Am I looking at another problem if it is not the sensor.

:liebe011:
 

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Discussion Starter #3
Changed the transponder on the gearbox tonight and it made no difference :crying: So what should I try next
 

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From Vag-Com:-

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1994-1997 C4 (A6/S6) Instrument Clusters
These have a high bit-error rate. We suspect they use a software-UART and "stretch" bits sometimes. The error-detection/correction logic built into VAG-COM's low-level protocol drivers as of version 0.70 seems to take care of this in a majority of cases, but I still had few reports of customers not being able to communicate with these clusters. In version 0.75 or newer, please ensure that Char Int on the Options Screen is set to approximately 3 (which is the default). On some PC's, it may be necessary to adjust this value to something other than 3. On very fast PC's try a higher value. On very slow PC's, try something less.

We have received reports from users who cleaned the terminals on the wiring connections at the back of their instrument cluster with electronics cleaner. This appeared to fix the problem with communicating with these clusters.


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I can confirm the above after getting a Vag-Com key usb with VAS 5051/2 and it works fine, has allowed me to reset the service interval, and adjust the injection timing that was retarded, along with clearing airbag & alarm error codes. It does however have com problems with the cluster, so I'll be cleaning the connectors as suggested. I managed to reset oil, ins1, (time and mileage), and ins2, (but I had to do the separately, and be quick due to the flaky connection)

Not sure if the Vag-Com info would relate to your car, but it might be related to your Speedo issue, and it wouldn't hurt to clean them, or could it be you have disturbed wiring or a connectors while doing all that work on the cooling / heating system. Check for bad / corroded pins in the plug that connects to the transponder to, and try to trace the loom back to see if there is any damage, (easier said than done I know).
 

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Discussion Starter #5
Spot again BladeRunner :) :)
Took the cluster off and cleaned the spiders out from behind. Gave it a good going over with cleaner and put it back. Seemed to be no different at first but I stopped and switched off and then restarted it seems to work normally now. Will borrow a GPS system to compare the speedo readings over weekend.
:liebe011:
 

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:beer: ....Need to do mine, not had your level of problem, but my Vag-Com connection issue means there is probably some degradation in the connectors. If your problem returns or is similar but less consistent try unplugging the connectors in turn, spraying with contact cleaner and then plugging / unplugging repeat many times and this should help "polish" the pins cleaner. If it doesn't help try moving and flexing all the wiring behind the dash around.

The speedo sender unit is supplied by E5, (earth point 5), via a brown wire, and pulses a ground or negative signal related to speed, via a brown /red wire to pin 8 of connector T26, at least according to the Haynes manuals "typical" diagram for the C4 A100 / A6

E5 also supplies the brake fluid sender unit, (whatever that may be), and the Tachometer, a bad earth might show some weirdness on these two as well...
 
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