I have no glow plug light showing when I turn ignition on

[mercmancdi]

06 face lift clk 320cdi v6 7 speed.
I have no glow plug light showing on dash when I turn ignition on yet
the icarsoft shows no fault.
Any way this only operates when exterior temperature drops to a certain level.

I should know this but just can’t think straight.

 

[whitenemesis]

Glow plugs also perform a post ignition function to reduce emissions, so should operate