No DRLs

[Mr.White98]

The DRLs don't work on my suburban and I'd like to have the circuit functional for a switchback mod I want to try. I've traced power up to the forward lamp harness connector and I have power from the DRL relay, but not to the low beam lamps. When I turn the headlights on, I have power at the forward lamp harness connector and at the low beams. Since the DRLs and low beams use the same wire coming out of the DRL relay, I'm stumped as to why I don't have DRLs.

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[shamrock246]

On mine it was the Diode 203 it's mounted to the dash frame with a big heat sink in about in the lower center of the dash total pain in the but to get to,Plus there interlocked thru the ebrake switch make sure that is working.Is the DRL indicator light on in the cluster?

 

[someotherguy]

If suspecting the DRL diode and you go to replace it, just be sure to have your battery disconnected when you do so. It hasn't happened to me, but someone whose experience I trust, says he blew one up installing it with the battery connected. I haven't studied the circuit enough to understand if this is possible but in a pinch, why risk it?

Richard

 

[Mr.White98]

DRL indicator turns on when I start the truck, stays on when the parking lamps are on, and turns off when the headlights are turned on. I don't suspect the diode since I have power to the DRL relay from the diode.

 

[someotherguy]

Again I haven't studied the circuit, and honestly that jpg is too small to really be useful. Have you determined 100% that the current flow supports your theory? The diode should be dropping the voltage to the headlights, that's the design of DRL, not full intensity in that mode. I would think the relay comes before the diode...but I could be wrong. It is somewhat common for the diode to be bad, which is why it's coming up as a likely suspect.

Richard

 

[Bob L]

Have you checked the fuse? I removed the fuse to mine and the indicator lamp is still lit when head lights are off but headlamps are not.

 

[df2x4]

The diode should be dropping the voltage to the headlights, that's the design of DRL, not full intensity in that mode.

Sorry to derail this slightly but I'm curious, is this something you've checked? I've seen a few people post this but I can't tell a difference between either of my 97s DRLs and low beams. Never got the multimeter out to check because it's across town in my broken truck.

 

[someotherguy]

Sorry to derail this slightly but I'm curious, is this something you've checked? I've seen a few people post this but I can't tell a difference between either of my 97s DRLs and low beams. Never got the multimeter out to check because it's across town in my broken truck.

That's what it's *supposed* to do...whether or not you can tell with the naked eye, dunno. Might take a professional light meter or some such...or even simpler, maybe a clamp style meter over the harness leading to the lights and compare to normal headlight function. It may also be that the current is PWM, which is why you see discussions about LED's (and I would bet HID's too) not being suitable for use as DRL's.

EDIT - yeah, just checked a spare manual I had laying around - according to the 1996 GMC Sierra user's manual, "The DRL system will make your headlamps come on at a reduced brightness when: * the ignition switch is on * the headlamp switch is off * the parking brake is released"

I had to check because I don't think it's necessarily a written rule that all DRL systems that utilize the low beams will operate them at less brightness than normal. It only made sense to me though because of the diode module. They're using it to step down the voltage, which is also why it's on that heat sink.

Richard

 

[someotherguy]

Have you checked the fuse? I removed the fuse to mine and the indicator lamp is still lit when head lights are off but headlamps are not.

Sound advice, even if you think you've already checked the fuse. The way the numbers are silkscreened on the fuse block, it's easy to find yourself looking at the wrong row. Fuse #15 is 3rd row down from the top, 3rd fuse "in" from the front of the truck.

Richard

 

[Bob L]

The reason I pulled the fuse on DRL is I like to be able to flash my lights to passing trucks or someone trying to turn left in front of you. With DRL activated I need to turn on lights then blink high beams, to much effort.