A6 - onboard computer problem, pls help me!

A6, 2,8 quattro, 1999.
Suddenly my trip computer started to give me very strange information about current fuel consumption. I.E. - my car is STANDING in "D"
position (red traffic light) and it shows 14,6L/100 km !!!! That is impossible !!!
Besides, it shows that current consumpt. is app. 3 times bigger than before. It shows some strange numbers (20L / 100km) even my engine is in "N" position for 15 seconds (!!!!!)
Can you help me please?
Few days ago I installed front parking sensors and CD changer. Is it possible that something happened with eletronic regarding to onboard computer????
Thanks a lot!
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