Pontiac Repair: 2001 pontiac bonneville 3.8, pontiac bonneville, upshift

Question
my moms car  the analog speedometer is reading faster than she is going. going between 90 to 120 mph when she is not going any way close to that speed. all the other gauges work fine. if you can help me fix it 4 my elderly mom i would be very thankful.

Answer
Hi John:

Well start from screatch does it have the cirrect tires on it Open the driver door and the sticker it will have the correct tire size for the car and look at the tires. If they are the same then on to step #2 does the car upshift at normal speeds? meaning dies it upshift really quick like you in 4'th geat before 35 MPH?  If not then My guess is that the vehicle speed input is correct in order to verufy this the car will have to be driven with a scan tool on it and see what the vehicle speed actaully is compaired to the speedo. and what the Anti lock brakes speeds are compaired to the vehicle speed and see if they match if they all match and the speedo is the only one that is off then I would say the issue is with the Insterment panel cluster is bad. good luck :)