2001 Chrysler PT Cruiser speedometer

Your "Vehicle Speed Sensor" is used by the computer to calculate actual vehicle speed and then passes this information on to your gauge.

Your "Crankshaft Position Sensor" sends r.P.M. Data to the computer, which then passes this information on to your tachometer.

But if your VSS was faulty, it wouldn't effect your tach. And if your CKP was faulty, it wouldn't effect your speedo.

So if both of these units are giving false information, I'd think you have a problem in the "instrument/gauge cluster control module", the wiring/connectors that exits your computer, or the computer itself.

You should first use a "Capable" scan tool to view your system monitors. (All scanners aren't created equal) This will give your readouts of your CKP and VSS to see if they are functioning.

If these sensors are operating correctly, then you should check the wiring/connectors at the back of the gauge cluster and trace them back to your computer.