2004 chrysler Pacifica speedometer

my step kid has 2004 Chrysler Pacifica the speedometer reads 15mph at a stop or in park & it way off going down the road & the transmission shifts fine it has no codes what would cause this ?:banghead:

You can run a self test on the cluster to see if it is cluster issue. All you do is with the ignition OFF, depress and hold the Odometer Reset button for 10 seconds then release the Odometer reset button. The cluster should enter a self test mode. All the indicator lights should come on and all the gauges will sweep. I cant seem to find the points where the speedometer will stop but after the self test is done, where the odometer is, it will show any codes that are set or were set during the self test.