Does your expedition have the large 4R100/E4OD or the smaller 4R70?
Monitor AC voltage out of the Vehicle Speed Sensor (on rear of transfer case on 4WD vehicles,) with a scope on the Gray/Black wire at 30 MPH while on a rack. Value should be greater than 3.5 volts AC. If no or low voltage out, inspect drive gear for being loose or damaged. If OK, replace VSS and retest. If voltage is OK, check it again under the same circumstances on the female side of connector C-172, terminal 20 (38 cavity connector on the RH side of the firewall). If the voltage is lower, repair the Gray/Black wire from there to the VSS. If good, move to connector C-159, the Brown 40 cavity connector on the rear of the LH fender and repeat process of checking the signal on the Grey/Black wire, each side of the connector, repairing as needed. If the signal is OK there, it next goes to terminal 21 of the CJB, connector C-243 where it travels by printed circuit through the box and internally connects to the GEM module, and also exits at terminals 14 to supply the signal to the instrument cluster.
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