Take the front panel off and on the top right hand corner is the control module. On the right hand side edge of the module is an LED light which shines through a plastic lense then is redirected by a prism & bounces back through a second plastic lense to a receiver on the module. If drawer is not closed or the lense or the prism is out of alignment it will think that the drawer is open. Had one once where the module case was broken putting the light out of alignment with the lense.
Lincoln Appliance NZ, May 2010