daytime running lights

[GnarliSafari]

the daytime running lights in my 99 recently stopped working, i noticed this the other night while pulling up to my garage in the dark and turning off the headlights, normally the daytime runners are always on headlights or not unless i apply the parking brake. after reassuring myself that the parking brake wasnt actually on i played with them a while and they still stayed off. the headlights and brights and turn signals all seem to be working fine no bulbs are burned out, mine is the older style where you still have to manually turn the headlights on at night but i no longer have the automatic daytimes. anyone ever have this problem or know what may be causing this? i never thought i liked the daytimes but now that i dont have them i am worried there is more to the problem.

[astrozam]

Checked your DRL fuse?

[GnarliSafari]

thats what i was wondering, i guess i probably could have just looked first but i did not know if such a thing even existed, i will look for it and that will hopefully be the problem, if it is maybe i will put a kill switch in for it.....thanks!!!!

[GnarliSafari]

well the fuse was fine, i replaced it anyways but still no go, hmmm....

[crash]

there's a relay in the drivers side B piller. i think it's called a relay.. or resistor or something like that. my drl's haven't worked since i got the 99. i took it all apart and other than looking at the stupid thing i just reconnected it and put everything back together. it's a royal pain to get at and remove. who knows why they would run it way the #%$ over in the B piller as opposed to behind the dash or under the seat or engine bay.... anywhere but the B piller...

[okeman]

think of the relay like a switch, if you have power in and none out its bad,

[astrozam]

well the fuse was fine, i replaced it anyways but still no go, hmmm....

I got to thinking a little more about this, when I built my upgraded headlight wiring harness last yr I noticed that when I hooked it all back up my DRL's didn't work ( as I hate DRL'S anyways ) this didn't particularly bother me,however I did want to know why they didn't work so I asked V8Famvan ( our resident gm mech ) we figured it out and what I didn't do was run the grnd from my new harness thru the DRL grnd, because of this the DRL'S did not work. Its possible that the grnd for your Drl's is toasted/broken/frayed etc, perhaps look in that direction as a possible cause.

[GnarliSafari]

well i may just leave it alone now that i know there are no known future surprises, i never much cared for them anyways but was a bit worried it may cause more problems down the line, thanks for all the helpful responses though.

[crash]

thanks for posting that image oke ... helpful

if I recall correctly.. the thing that i removed and checked out had a big heatsink on it... :-k

by the way, if we're talking the same part.. as far as I understand it's a GM only thing

[astrozam]

if I recall correctly.. the thing that i removed and checked out had a big heatsink on it... :-k

The drl's just run off a reduced voltage from the ( high beams, I think :-k ) anyways i'm pretty sure all they are is basically a big resistor with its own heatsink to dissipate the heat,so the thing you found was most likely it Rob.

[phr1$k37]

if I recall correctly.. the thing that i removed and checked out had a big heatsink on it... :-k

The drl's just run off a reduced voltage from the ( high beams, I think :-k ) anyways i'm pretty sure all they are is basically a big resistor with its own heatsink to dissipate the heat,so the thing you found was most likely it Rob.

I think '96+ it was a reduced voltage on the lo-beams as were mine ('97).

[Astrophysics]

the DRL in line device with the heat sink fins and the sharp edge sheet metal bracket is actually 2 silicon semiconductor diodes in series. Each diode has about 0.7 VDC drop so the 2 diodes in series drop about 1.4 VDC to effectively dim the light for use as a Daytime running light. You can order the DRL diode for about $40 from gmpartsdepartment.com or gmpartsdirect.com.
I changed the bad on on my 99 Yukon. I recommend that when you remove the old one just leave off the old sharp sheet metal mounting bracket and secure the new DRL diode part with 2 heavy duty plastic tie wrap cable ties.

Astrophysics.

PS

if you take running voltage of 14 VDC and assume low beams are 50 Watts each for 100 WAtts of power, then use Ohms law to calculate the current flowing, one gets about 7 amps of current.

then do the circuit analysis: 14 VDC - 1.4 VDC (diode drops) - 0.5 VDC (IR drop in the OEM wiring harness) = 12 volts to bulbs (instead of 13.5 VDC) So 1.4 VDC is dropped in the diode and the current flow is about 7 amps so power disipated in the diodes is high and the heat sink fins are needed to cool the diodes. Power disipated in diodes : IR = 1.4 VDC = (7 amp *R)
R= 0.2 ohm approx. so Power = I squared R = 7*7*0.2 = approximately 10 Watts. So those diodes get pretty hot and eventually burn out.

[crash]

yikes... ..

so in short .. for the layman. if I pull this thing out again and post pics can you show me what i need to test/replace?

[Astrophysics]

I will try to take a digital photo of the DRL diode part. It is about 1 1/2" x 1 1/2 " x 1" outer dimensions, and has a built in connector with 2 contacts. Basically if you look in the schematic drawing in your shop manual (Haynes or Chilton) you should be able to follow the low beam light wiring cicuit to the DRL diode.

I have had good luck calling the local Chevy dealer or visit them and ask them to print out the exploded parts diagram showing where under the dask the DRL diode is located.
go to http://www.gmpartsdepartment.com and enter your car year and model and search for electrical parts... to find lights....daytime running lights etc.
or they usually will fax the info to you.

Astrophysics.

[v8famvan]

Here is the GM service manual diagram for replacement of the DRL diode in the back of the previously mentioned drivers side 'B' pillar.