My 1990 535 5spd has had a weird issue since I bought it. None of the mileage related functions of the OBC ie range, avg Mph, etc work, nor does the cruise control and all the wiper settings seem to be as if the car doesn't think it is moving ie intermittent is very slow, low speed is intermittent and then high speed is normal. From reading through archives and my manual this would seem to point to a speed sensor error in the diff but the speedo and mpg gauge in the dash both work fine. Am I correct in assuming they get the signal from the same source? Does the signal go to the dash first and then OBC so maybe there is a loose connections somewhere? Thanks for any help you can provide