remote door locks do not work at low temperatures on 2002 Mercedes-Benz S430

Using remote the locks work fine until outside temperatures get cold.

Asked by for the 2002 Mercedes-Benz S430
There may be moisture in the pump or vacuum lines, did you try using the blade key in the truck to check operation, if that works the fob batteries may be weak.
Thanks. I"ll look at that. Pump located under rear seat?