Headlights on high beam for extended period of time. begin to flash headlights on and off. Eventually staying off.

Ive changed the relay and the headlight switch on the dash .. still wont turn off headlights ? Just changing parts won't fix it , need to test . Hooking up a professional scan tool , one that can read codes in the BCM - body control module is the way to start to find the problem . Then familiarize yourself with how they work.

Headlamps
Major components of this system are the body control module (BCM), headlamp relay, beam select relay, ambient light sensor, headlamp and panel dimmer switch, turn signal/multifunction switch, park brake switch, and the low and high beam headlamps.
The headlamps may be turned ON in 2 different ways. First, when the driver places the headlamp switch in the ON position, normal operation occurs. Second, when the headlamp switch is placed in the AUTO position, automatic lamp control (ALC) operation occurs. During ALC control, the headlamps will be OFF in daylight conditions or in low/high beam operation in low light conditions.
The headlamp relay receives battery positive voltage directly from the battery. The BCM supplies a ground signal to the headlamp relay for normal headlight operation. The BCM also supplies voltage to the beam select relay coil for high beam headlight operation. When the driver places the headlamp switch in the ON position and the dimmer switch is in the low beam position, the headlamp relay supplies current flow through the left and right low beam headlamp fuses to both low and high beam headlamps. Both low beam headlights are grounded through the beam select relay. When activated, the dimmer switch sends a ground signal to the BCM in the high beam position and a momentary ground signal in the flash-to-pass (FTP) position from G106. The BCM then energizes the beam select relay which switches the headlamp grounds from the low beam headlight bulbs to the high beam headlight bulbs illuminating the high beam headlights. With the headlights in the low beam position, the high beams may be momentarily turned ON or flashed by activating the FTP portion of the switch.
The instrument panel cluster (IPC) illuminates the high beam indicator when the BCM detects that the high beams are requested. The IPC receives a class 2 message from the BCM requesting illumination.
The Headlamps On at Exit and Perimeter Lighting modes can be adjusted using the steering wheel controls to select the function as displayed in the driver information center (DIC). The Headlamps On at Exit selection will allow the driver to customize the period of time that the headlamps remain illuminated upon exiting the vehicle. This period can be adjusted from 0-180 seconds. The Perimeter Lighting feature allows the driver to select if they want the headlamps and backup lamps to illuminate when the door UNLOCK button on the key fob is activated. This feature can be turned ON or OFF by using the DIC steering wheel control buttons.

DTC B2575 Headlamp Control Circuit

Circuit Description
When the body control module (BCM) senses a request for headlamp or daytime running lamp (DRL) illumination, the BCM sends a ground signal to the headlamp relay through the low beam headlamp relay control circuit. The headlamp relay will illuminate the low beam headlamps.

Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, command the headlamps ON and OFF.
Does the headlamp relay turn ON and OFF with each command?

Do you know what bi-directional control means ? Need a professional scan tool to do these type of test .

DTC B2602: Daytime Running Lamp Control Circuit Low or Open
DTC B2603: Daytime Running Lamp Control Circuit High

Without this type of info. from service repair manual an using a scan tool your missing the big picture .

i don't know. perhaps having both beams on that long may draw too much electricity. please repair the high beams
so they light without delay. an auto wrecker yard might let you switch out parts from one of their used vehicles.

It could be driving lights mode instead of low beam. Check connections.

Bad switch or relay.

Best guess is the Hd. Lt. Relay.
Probably will have to be replaced.

bad headlight switch

Could be a faulty dimmer switch or short in the circuit.

Removal & Installation To Remove:
WARNING
The halogen fog light bulb contains gas under pressure. The bulb may shatter if the glass envelope is scratched or if the bulb is dropped. Handle the bulb only by its base. Avoid touching the glass envelope.
NOTE: The headlight bulb should not be removed from the headlight assembly until just before a replacement bulb is installed. Removing the bulb for an extended period of time may affect headlight bulb performance. Contaminants may enter the headlight assembly where they can settle on the lens and reflector. Never turn on the headlights with the bulb removed.

1. Before servicing the vehicle, refer to the precautions in the beginning of this section. NOTE: Make sure that the headlight switch and the ignition switch are in the OFF position.
   
2. Remove the pin-type retainers, screws and the air deflector from the radiator.
3. Remove the three bolts and the headlight assembly.
4. Disconnect the electrical connector.
5. Remove the cover from the rear of the headlight assembly.
6. If equipped with HID, release the spring tabs to remove the low beam bulb, otherwise disconnect the electrical connector and remove the bulb.
7. Disconnect the electrical connector and remove the high beam bulb.

HID low beam headlight bulb

Standard low beam headlight bulb

High beam headlight bulb

To Install:

1. Place the headlight assembly in the proper position.
2. Install the cover from the rear of the headlight assembly.
3. Connect the electrical connector.
4. Install the three bolts and the headlight assembly.
5. Install the radiator air deflector.

this could be a little more simple depending on the lighting outside. quite a few GM's with DRL will turn on the dash lights and tail lights automatically when it gets so dark outside. if it happens when it's completely dark out i would check the switch itself and maybe the relay incase it is sticking

u are going to have to replace the turn signal switch to correct this.