I have 2 nav units, ones a 2008 factory Ford that had a software hack, though it does require a few keystrokes every start up to enable the hack. And a aftermarket pioneer avic F90bt that had a VSS (vehicle speed sensor) wire that was left disconnected so that it would not lock up in motion. Both units actually have VSS wires. My bet is that this TOMTOM UNIT use both GPS and VSS. When GPS signal is lost the NAV unit knows vehicle speed and can give accurate ETA's and whatnot. The VSS is definately the culprit of the lockout, find the VSS wire cut it, problem solved. As with the Ford nav, there was a software disablingway of disabling the VSS, so this one prob has a way also.