Evenexchange

The other day I took my car on a longer than usual trip, accompanied by my GPS.
My GPS will read that I am going 55mph, while my speedometer reads that I am going 60mph.. My car thinks that I am going 5mph faster than I really am. What could be causing this? I have not modified any drive shaft or rear end components, and have the stock gearing as far as I know. This car has had 3 owners before me.

The only thing that I can think of that might have to do with something is that the gauge cluster is not stock and the temperature gauge reads extremely hot, when it's not. The car has been tested at the dealership and runs normal at like 170 or something.

PaintballFreak

Try getting a friend to drive next to you on the highway. Get him/her to set the cruise control to a speed you decide beforehand, give you the thumbs up, and then you try to match it. Then see what your speedometer reads. I wouldn't trust your GPS unit to tell you what speed you're going over your speedometer. I would say it's more likely that your GPS unit is a little off.

ct_white_stang

No, this is what you want to do. I just went through this. If it is determined that it is off you will have to pull the cluster out and set by hand, once you are in diag mode you are looking for the eng setting. Its easier then it seems. You will need a helper though.

http://www.paladinmicro.com/PalMFrame00.htm?wks=hec

PaintballFreak

Ah I missed the aftermarket cluster part. First do the drive test to see how much it is off. Then you'll have to adjust the needles.

cliffyk

GPS receivers (all of them) are accurate to within 0.1 MPH, and have been for several years since the deliberate timebase manipulation done for the civilian channels was turned off. The math for calculating speed from positional changes over time is simple, a GPS maker would have to deliberately make it calculate incorrectly.

What the OP needs to do is set the instrument cluster to the diagnostic mode (click here for more) and compare the digital readout with the gauge and GPS.

If the digital speed and the gauge do not match, and the digital speed and the GPS do, then the speedometer needle has been incorrectly positioned.

If the digital speed and the gauge match, and do not match the GPS, then the final drive gears may have been changed--going from 3.27:1 to 3.55:1 would make the speedometer read 5 MPH fast at 55...

gec

Run into this all the time with customers...bigger wheel and tire (overall diameter) if larger will throw off a minor amount. If you want to fix it like the others said you have to replace the pin. Click on the link in my sig and there is a video on gauge led's that will walk you through that process. Kenny