NAV dead reckoning



Our NAV unit's dead reckoning sometimes goes completely awry and ends up going all over the place even if we're driving relatively straight roads.
This usually when we drive in an area where our maps are out of date. A highway was re-aligned, and if we have no satellite connections, then all of a sudden we're drving all over the ocean and points less known.
Is the dead reckoning calculated by the NAV drive itself, or is this function addressed elsewhere in the vehicle?





