Intermittent headlight issue

[dmillion]

Sure could use some help on this one. My 2014 GMC Sierra SLT headlights will come on and go right back off at times. Sometimes they will stay on. Fog lights work fine. I have replaced the relay and have looked for a fuse which I cannot find in the engine compartment or either fuse panels inside the doors. It’s driving my crazy.

Edited November 20, 2021 by dmillion
More detail on truck model

[JimCost2014]

2 hours ago, dmillion said:

Sure could use some help on this one. My 2014 GMC Sierra SLT headlights will come on and go right back off at times. Sometimes they will stay on. Fog lights work fine. I have replaced the relay and have looked for a fuse which I cannot find in the engine compartment or either fuse panels inside the doors. It’s driving my crazy.

Welcome to the site.

 

You may have a bad under hood fuse box, not serviceable, will need to be replaced. Know this from experience with my 2008 (not headlights, 3rd brake light).

 

Low beams are wired direct from bcm. High beam control relay is in the under hood fuse/relay box which are "non-serviceable Printed Circuit Board (PCB) relays and are internal to the block".

 

The headlamps may be turned ON in 3 different ways:

•When the headlamp switch is placed in the ON position, for normal operation
•When the headlamp switch is placed in the AUTO position, for automatic lamp control
•When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay
The BCM will also command the low beam headlamps ON during daylight conditions when the following conditions are met:

•Headlamp switch in the AUTO position
•Windshield wipers ON
•Vehicle in any gear but PARK
When the BCM commands the low beam headlamps ON, the vehicle operator will notice the interior backlighting for the instrument cluster and the various switches with backlighting control will dim to the level of brightness selected by the instrument panel dimmer switch.

The body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor to determine if headlamps are required or if daytime running lamps will be activated based on outside lighting conditions. When the headlamp switch is placed in the OFF position, the headlamp switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the headlamp switch in the PARK position, the headlamp switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is placed in the HEADLAMP position, both the headlamp switch park lamps ON signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM responds to the inputs by illuminating the park lamps and headlamps. When the low beam headlamps are requested, the BCM applies B+ to both low beam headlamp control circuits illuminating the low beam headlamp.