Audi Coupe Quattro Trip Computer

my CQ has a trip computer, but the readings are all 'zero'. The control switch works fine, I can cycle through the different values, but they're all
zero... Any ideas where to check? I'd say the connections on the instrument cluster, but I assume these are fine since I can control the computer using the switch. So my guess is that the computer is not getting readings for my fuel consumption and/or distance driven. Does it get this from the ECU or should I check some connections in my engine bay or somewhere else? thanx for your help!
1990 Coupe Quattro 2000 Audi TT Quattro
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