Daytime running lights won't come on fuses check out good and relay good for a 2001 gmc sierra slt

If the headlamps on your 2001 GMC Sierra won't turn off when the truck is started, there are a few potential causes for this issue:
1. Faulty headlight switch: The headlight switch may be malfunctioning, causing it to remain in the "on" position even when the truck is started. A faulty switch can prevent the headlamps from turning off as intended.
2. Stuck relay: There could be a stuck relay in the headlamp circuitry, keeping the power to the headlamps constantly engaged. A stuck relay can cause the headlamps to remain illuminated even when the switch is off.
3. Wiring issue: There may be a wiring problem, such as a short circuit or a damaged wire, that is causing a constant supply of power to the headlamps. This can prevent the headlamps from turning off when the truck is started.
4. Daytime running lights (DRL) malfunction: If your Sierra is equipped with daytime running lights, there could be a malfunction in the DRL system. This can cause the headlamps to stay on at all times, regardless of the switch position.
To address this issue, you can try the following steps:
1. Check the headlight switch: Inspect the headlight switch for any signs of damage or wear. If the switch appears to be faulty, it may need to be replaced.
2. Check the relays: Locate the relays associated with the headlamp circuit and check if any of them are stuck or not functioning correctly. If a relay is found to be faulty, it should be replaced.
3. Inspect the wiring: Thoroughly inspect the wiring harness and connectors in the headlamp circuit for any visible damage or loose connections. If any issues are found, the wiring should be repaired or replaced as necessary.
4. DRL system troubleshooting: If your Sierra has DRLs, consult the vehicle's owner manual or a service manual to understand the DRL system's operation. Follow the troubleshooting steps outlined in the manual to diagnose and resolve any issues with the DRL system.
If you're unable to identify or resolve the problem on your own, it is advisable to consult a qualified mechanic or take your GMC Sierra to a reputable auto repair shop for further diagnosis and repair.

It could be the sensor on the top of the dash,fuse, relay, or the BCM

You might want to start by checking the fuses associated with your headlights. If those are fine, check the headlight relay. You can do a search online to see where the relay is located on your vehicle.

Their is a photo light sensor someware on the top of you dashboard or on backside of rearview mirror that has been covered possibly dash mat ? something hung on your rearview mirror.let me know.

you will see 2 pins or clips on back of headlamp asm, remove them and lamp asm pops out , now remove bulb, good luck.

you have a ground problem , if alt output is good...please rate my help, thanks...

Yes it has a rubber cover over it in the engine compartment.i would change the relay.good luck.

make sure parking brake pedal pulled up all the way

Did you check your fuses by any chance? otherwise check all your connection from the headlights back. Check your relays also.

Make sure that ypur parking brake is completely released because if it is engaged even slightly the daytime lights will trun off. If that's not the problem then check the bulbs.