No Headlights

[franco408]

I have a 2001 Yukon Denali I got no headlights no low beam no high beam and no day light running lights. I have parking lights turn signals and rear lights. The high beam indicator light on the dash is on and won't come off. Seems like once that light came on the dash that's when the headlights went out. Checked fuses, visually checked around for any bad wiring. I go further into the diagnosis tomorrow morning any suggestions will be appreciated. Thanks

 

[rockola1971]

The high and the low do NOT share the same ground so I believe you can rule out a ground problem. So we will go after the hot side. Your headlight switch position makes a difference as far as what all comes into play. In On mode your BCM is bypassed and the switch directly feeds power to the headlamp relay coil effectively bypassing the day/night sensor circuit in tandem with the BCM. In auto mode your BCM comes into play and energizes the headlamp relay when the BCM is in night mode via the Day/Night sensor (thats the little smoked globe lens on top of the dash near the windshield).
There is more than one fuse that will kill your headlights. Double check Fuse marked TBC 10a (under hood). This is the fuse that feeds both of the above modes (Auto and On) and does nothing more than provide power to the headlamp relay coil. Without this fuse being good or associated wiring you are without headlights. If that all checks out then.....
I would suspect the headlamp relay itself. [during this check your headlight switch must be in on mode instead of auto] Check for power at the fuses marked LT HDLP and RT HDLP.(both sides of the fuse) Your headlamps are fed power actually by these two fuses (one for left side and one for the right side) but these fuses will be dead if the headlamp relay has a bad coil, no power to its coil, burnt internal contact (these contacts feed LT and RT HDLP fuses). It is unlikely that both the left and right side headlamp fuses blew at the same time unless you have a major wiring problem.

I suspect the above will find your problem. If it doesnt then post all results you find for the above. You could have a bad headlight switch, bad wiring, etc. If you are lucky you just need a new headlamp relay. Any auto parts store will have it if thats the culprit.

 

[franco408]

Thanks for all your detailed help. I'm about to take a look at it right now. I really appreciate your help I'll let you know any results I may find soon.

 

[Rocket Man]

I second the headlight relay. Mine did the exact same thing when my relay was loose in the socket. Try reseating it or swapping it for one of the other ones that are the same part.

 

[Dcicirelli]

Thanks for lead on what fuse feeds the relay coil. Mine was blown and when I replaced it the lights came on just for a second and went back off. Further troubleshooting revealed the ground to the coil had opened kind of weird I’m gonna have to look further but at least my lights are working now I put a jumper in from the body to the ground terminal on the relay

 

[Dcicirelli]

Thanks for lead on what fuse feeds the relay coil. Mine was blown and when I replaced it the lights came on just for a second and went back off. Further troubleshooting revealed the ground to the coil had opened kind of weird I’m gonna have to look further but at least my lights are working now I put a jumper in from the body to the ground terminal on the relay

 

[Dcicirelli]

So… while one my 1st night drive my lights were working fine. After about 20 minutes of “lights on” the 10 amp fuse that feeds the headlight relay blew again. Before all of this, I installed a new aftermarket light controller to restore my dashboard lights and that is when the headlight issue started. The controller was getting warm and I think it is faulty. I am going to get one from the junkyard and see what happens…. Cheers!