Rear Window Defoggers System: Operation

Ignition switch must turned to ON position and engine speed greater than 400 RPM. Turning rear window defogger switch on will supply a ground signal to instrument cluster. Rear window defogger switch is hard-wired to instrument cluster. Instrument cluster sends an on command to Front Electronic Module (FEM) and supplies power to illuminate rear window defogger switch indicator in climate control assembly. FEM will then verify Powertrain Control Module (PCM) engine speed signal is greater than 400 RPM. If RPM signal is verified, FEM energizes rear window defogger relay which supplies power to rear window defogger grid. Rear window defogger will operate until turned off or for 10 minutes then automatically turn off, through accessory delay relay. Timed intervals can be repeated as necessary.