Re: 2001 Jeep Grand Cherokee Speedometer Inaccurate
Welcome to the garage.
The vehicle speed signal comes from both rear wheels speed sensors, which are used by the ABS system. The ABS controller sends the speed signal to the PCM and then the PCM will send it over the PCI data bus to the instrument panel. I would start doing the instrument self test to see if the instrument cluster is not faulty: with ignition in OFF, push the odometer reset knob and while pushing, switch the ignition to RUN. Now the instrument self test will begin, all indicator lights should come on, odometer will count 00000000, 11111111, 22222 etc and all the instruments should go to full scale and then return to the normal position. If the speedometer now also only goes halfway, its most probably time for a new cluster.
As soon as the test begins, you can release the knob.
I presume that the ABS fault light is not lit on the instrument panel.