2002 speedometer consistantly reading fast...

I have a 2002 Buick Century Limited with 75K miles. It has stock wheels and stock size tires with decent tread left. The problem is that the speedometer reads about 2.5mph FASTER than I'm actually going. (I have used two different GPS's to check this.) I have searched this forum for "speedometer" and have not found anyone with a similar problem since mine is consistent, and not intermittent. It's off the same at low speed as it is at high speed, the needle never jumps, and it has never stopped working all together. Anyone have any idea what could cause this? Thanks for your help.

It may be caused by the speed sensor being out of calibration. Your dealer can check the calibration or you can take it to a shop that specializes. This is a common problem and most of the car speedometers are not exact.

Thank you very much for your reply. I'll have it checked out.

Hi,

An automated speedometer calibration technique includes a calibrated supplier to produce input signals for the speedometer. At the time of calibration, the magnetization of the fixed magnet in the meter is altered until the exact deflection is acquired.

You need to contact auto vendor so that they dispatch technician to rectify the speedometer.

Remove the cluster. Unlatch the faceplate side.
Use a fork under the gauge needle to slowly pry it up. You can use a piece of tape under the fulcrum point of the fork to protect the gauge face.

Put the cluster without the faceplate back in the dash and plug in the connector.
Ignition off, put the needle back on the gauge lightly at the 0mph mark.
Take it for a drive on a flat road with your GPS, pick a speed and set the cruise control.

Check the difference between the gauge and the GPS.
Stop the car and turn the ignition off. Pull the needle straight off then put it back on at a spot plus or minus the distance it was off at speed. Repeat the test until you're satisfied with the accuracy.
Ignition off, press the needle down fully until it stops. Make a final test drive.

Remove the cluster, clean and replace the faceplate. Make sure all the latches on the faceplate are locked in, reinstall the cluster.

Or;
Send it to one the many speedometer repair shops on eBay.
http://motors.shop.ebay.com/eBay-Motors-/6000/i.html?_nkw=speedometer+repair+century&_trksid=p3286.m270.l1313&_rdc=1

Or;
http://www.mrwhizard.com/

http://www.speedotest.com/

As mentioned, your VSS calibration needs to be set correctly within the PCM. Ask your dealer if they can assist, or find someone with correct tuning software (program) to calibrate.