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jeb

Daytime Running Lights not working

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DAYTIME RUNNING LAMPS (DRL)

The daytime running lamps (DRL) will operate when the ignition switch is in the RUN position, for automatic transmissions (A/T), the gear selector is not in the PARK position, the headlamp switch is in the AUTO position, and for manual transmissions (M/T), the park brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate. The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal it will either turn on the DRL or the headlamps for auto headlamp operation. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. The DRL can be manually turned OFF by depressing the AHL/DRL switch in the headlamp switch. The AHL/DRL defeat switch sends a ground signal through the DRL switch signal circuit to the BCM. The BCM then turns OFF the DRL and headlamps switch to manual control. When the AHL/DRL are manually turned OFF at the headlamp switch, the AHL/DRL will default to ON with the next ignition cycle. The DRL are separate lamps independent of the headlamps. With the headlight switch in the AUTO position, the DRL will either be turned ON or OFF, after an approximate 8-second delay depending on whether daylight or low light conditions are sensed. The DRL 10-amp fuse in the underhood fuse block supplies battery positive voltage to the DRL relay switch contacts and relay coil. When the BCM energizes the DRL relay , the DRL receive voltage on the DRL supply voltage circuit. Ground for the DRL is at G100.

 

 

 

 

 

2004DRLschem1.gif

Edited by txab

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Thanks. I'll find some time to see if I can trace it back. Looks like the BCM relay might need a look. But you'd think that since the DRL's do work for the lock/unlock, that'd be okay, too.

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Did you buy this truck used? It sounds like somebody monkeyed up the DRL circuit. They should not be acting that way.

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Nope. As I said above, I bought it brand new. Been a great truck.

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I have a 2008 gmc sierra 1500 and I am the second owner. I just bought the truck and recently noticed that the driver side DRL light won't come on, but the passenger side does. Like you said about them flashing when you lock/unlock the doors, mine does the same, they flash but but when I turn the one won't stay on? I am totally confused about what is happening. I have been through it a million times and will take it in, maybe someone else can figure out what I can't!

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I found out it was just a fuse under the hood that I didn't check #26 (Driver Side Park Lamps) also the (passenger side park lamps) in your case is #27 if you haven't checked those under the hood that could be it!!

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I found out it was just a fuse under the hood that I didn't check #26 (Driver Side Park Lamps) also the (passenger side park lamps) in your case is #27 if you haven't checked those under the hood that could be it!!

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Thx for listing the conditions the DRL's are on for, as I was incorrectly assuming they would be on with the engine [and was checking with it in Park, so no power to either plug, but fuse and relay were good, so I was about try digging into the wiring harness]. Thankfully, I googled for DRLs not working and came across this thread.

 

Now, I put on the parking brake, put it in gear, and like magic, power to the DRLs. One DRL was working fine, and the other has an iffy socket [there seems to be a bunch of burnt resin in the socket and both sockets and blubs look like they've been getting too hot]. I might have to go to the men's mall and get some replacement sockets, but it seems like they weren't designed right [as the bulbs should be able to be on all day without overheating the socket].

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