Mars does not have a global magnetic field which guides charged particles entering the atmosphere. Mars has multiple umbrella-shaped magnetic fields mainly in the Southern Hemisphere, which are remnants of a global field that decayed billions of years ago.
This article states that the maximum local magnetic field on Mars is 1500 nanotesla. This answer states that older crust typically has a magnetic field of 15-20 nanotesla, with younger crust less than 15 nanotesla. Another answer claims ">1" nanotesla.
Suppose we landed a rover in a region with a 15-20 nT magnetic field. Would a rover be able to reliably navigate (i.e. know which way is "north") using these local magnetic fields? Or is there some issue that would make such navigation unreliable?
(We can assume that the rover won't travel far enough to leave the local magnetic field.)