2004 monte carlo - at night - car will start but NO headlights or dashlights
 

Hello:
I own a 2004 monte carlo ss for the last 3 years. every so often, when starting the car at night, the car starts but i have NO lights at all headlights or dashlights. IF i pull the knob on the headlight switch all lights come on, and if i push the knob back in, then the lights stay on in automatic.
But last night, which was cold at 35deg, i started the car and got same no lights and did as indicated above BUT when i pushed the H/L switch stalk back in to auto setting, i got an SES light on the dash!! Thats a new one.
I am wondering , is this an ignition switch prob, or DLR sensor or relay, or a bad h/l switch. Any assistance would be appreciated before i take my ride into the mechanic shop.

Thanks

hard to say without further information.

the system works like this:

the light sensor, headlight switch and signal stalk all are inputs to the body control module. the module control lighting output base on the inputs received.

so maybe the bcm is not seeing a input or the bcm is seeing the input but not able to turn the lights on.
diagnosis starts by:
-checking for codes in the bcm
-checking the inputs to the bcm with the scan tool.