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Originally Posted by pez
ya mine is about 4 mph slow, and I have stock wheels..The funny thing is if I hook my laptop into the obd the ECU shows the correct speed but the dash is off.
I dont know how true it is but I read somewhere that the acceptable tolerance is +/- 5mph which I thought was crazy for German engineering. But again I dont know how much truth is to that.
The dealer should be able to tweek it so it reads correctly. If that is something that is covered, that I don’t know I would say that it would be but if that crazy tolerance thing is true you might have to wheel and deal to get it fixed..
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Hi,
You are correct, the Speedo readout adds what Porsche Calls a
Safety Margin to the True speed.
If you own a '97-'00 Model, you can access the True Speed (in kph) through the Diagnostic Program Datastream hidden in your AC Climatronic Unit. It is
C code 20c. This value is True Speed w/o the added Safety Margin. This code only updates once/sec. Hope this helps...
Happy Motoring!... Jim'99