Worth bearing in mind that the OAT signal actually goes to the vario and
not the LX main unit.

The spec of the probe was changed a few years ago when some new vario types
were introduced (we had to fit a new probe when we upgraded to the V9
vario) so if you have changed the vario recently you may have the wrong
probe.

Also make sure the probe cable hasn't been cut and repaired, my
understanding is that you can't do this as it changes the resistance of the
unit and throws the readings off so if it has you need a new probe.