Our driver's side mirror has stopped adjusting right to left. Up and down adjustability is still working. Not frozen- not cold enough. Any ideas out there?

 

Bad switch contacts (rare) or broken wires going through the door's wiring boot (more likely) are by guesses. The mirror motor could also be shot.

 

But I can hear the motor working - just that the mirror won't go right or left. Do these pop out just like the VW ones?

 

just pops out try to push it in, mine pops out sometimes and won't move until you thrust it back on its mounts. pull the mirror off, with a little force it pops off. then try all the functions you will see if the motor moves the mount. then you will know whats up.

 

Could be the "position" sensors inside mirrors. They are 2 potentiometers for each one of X and Y axes. They transmit the position of mirror glass, information used for positioning.