Low Beams Don't Work [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Low Beams Don't Work


kurtgeiger
04-30-2007, 10:15 PM
2004 TB EXT with low beams that stopped working. checked fuses, bulbs...both OK. DRL's don't work...but highbeams work... HELP! is there something else that needs to be looked at?:crazy:

RozmerJJ
05-01-2007, 07:59 AM
Headlight driver module #46 in the under hood fuse box. This can be swapped with #45 I believe as a test only. IIRC #45 is the fan clutch which uses the same driver module as the low beams.

vball61
05-01-2007, 08:04 AM
Make sure that the 15A HDM fuse #53 in the underhood fuse block is okay. Beginning in late production 2004, that fuse supplies the solid state relay which feeds both of the the low beam headlamps.

Next thing I'd check is the solid state HDM relay #46 in the same fuse block. You should be able to swap it with the cooling fan relay (#45) to see if it works.

(Dammit, Rozmer, beat me to it...)

kurtgeiger
05-01-2007, 08:46 PM
:thx

Tried your suggestions....it was the HDN relay #46 that was bad! Appreciate your help!

RozmerJJ
05-02-2007, 07:14 AM
Not a problem....Glad to help!

:thumbsup:

Inko
05-30-2007, 09:28 PM
First, this is my first post. :).

I stopped by the dealer, who took an hour looking at it (I had to run to an appointment) and they couldn't find the problem. So, it leads me to believe that the above posts/fixes might not do the trick.

Because I am over 50K in mileage, I don't want to spend $$$ on dealer repair so I asked my local mechanic (who had to replace my brakes and rotors--second time since leasing the damn machine in 11/03--but that's another story) if he could take a look.

I had to leave it with him today and just got a call. He can't fix it either.

Long story longer: I will try the above-mentioned idea tomorrow but if there are any other suggestions, I'd love to hear em.

04 TB LT.

Thank you!

Inko

vball61
05-31-2007, 09:09 AM
It could possibly be a failure in the Body Control Module (BCM) output that drives the solid-state relay. This is a pulse-width modulated (PWM) output that, based on duty cycle, determines whether the low beam headlamps are driven at full brightness, or dimmed for DRL usage.

The BCM will set a DTC, #B2575, if it senses an open or short to ground of that output circuit. I do not know what, if any, diagnostics the BCM can perform to detect failure of the output itself.

Here's one way to check whether the BCM low beam headlamp output has failed...
Key off.
Disconnect the 24-way gray connector from the BCM (module is located under the rear seat on the driver's side)
Short the PINK/WHITE wire at pin A5 of the 24-way gray connector to ground. (Be careful not to spread the terminal...)
If the low beam headlamps turn on, I suspect that your BCM's output has failed.

Inko
05-31-2007, 09:12 AM
Thanks Vball. Will give that a try today and report back.

Inko

tblazed
05-31-2007, 09:21 AM
Short the PINK/WHITE wire at pin A5 of the 24-way gray connector to B+. (Be careful not to spread the terminal...)
If the low beam headlamps turn on, I suspect that your BCM's output has failed.

Actually, you would "short" the pink-white wire to ground to turn ON the low beams. High (12V on that wire) is off, low is on. The 12V comes from an internal pullup resistor in the headlight driver module.

Based on previous posts about this problem, most likely the problem is the headlight driver module "HDM" #46 in the underhood fuse block. As mentioned before you can temporarily swap 45 ( the fan clutch driver module) and 46, as they are the same.

vball61
05-31-2007, 09:29 AM
tblazed is correct. Got to it before I could correct my error... Fixed it.

rbarrios
05-31-2007, 01:16 PM
you guys are good with that info!!!!

Inko
05-31-2007, 04:45 PM
tblazed and previous posters.

I switched 45 with 46. It did solve half the problem. The low beams worked with the light switch in the "on" position. However, the DRLs do not work.

A previous poster suggested checking the "15A" HDM fuse. However, slot 53 on my cluster is for the electric Adjustable Pedal. I did not find an HDM fuse on my schematic.

As for Tblazed other suggestion regarding the BCM, you think too much of me. I am way not that smart to be splicing and grounding. (yes, I am one of those...lol).

At any rate, this forum has helped solve the problem. I don't need DRL's. Can I buy a HDM relay #46 in the aftermarket?

Finally, this is probably for another forum, but I really want to trade up to the SS, but they're quoting me now at over $500/month, 36month, with $5G's down. Given the marginal inconveniences I've had with the 04LT, first, I think it's overpriced, and second, even if it there was a price break, would you guys take the plunge?

Thanks again for your help. Looking forward to contributing myself.

Inko

tblazed
05-31-2007, 05:24 PM
tblazed and previous posters.



As for Tblazed other suggestion regarding the BCM, you think too much of me. I am way not that smart to be splicing and grounding. (yes, I am one of those...lol).

At any rate, this forum has helped solve the problem. I don't need DRL's. Can I buy a HDM relay #46 in the aftermarket?


Inko

Wasn't my suggestion to ground anything but that's OK ... that driver module is probably going to be a dealer-only item someone like NAPA might be able to get it the part number is printed on it. With the two swapped you won't have control of the fan clutch and it will set a code. I have no idea why the DRL won't work with the "good" driver module in the headlight circuit. The DRL signal comes from the BCM.

Inko
05-31-2007, 08:41 PM
Thanks again.

Inko

vball61
06-01-2007, 09:28 AM
A previous poster suggested checking the "15A" HDM fuse. However, slot 53 on my cluster is for the electric Adjustable Pedal. I did not find an HDM fuse on my schematic.

Make sure that the 15A HDM fuse #53 in the underhood fuse block is okay. Beginning in late production 2004, that fuse supplies the solid state relay which feeds both of the the low beam headlamps.
On early production '04 models, this fuse was used for the Adjustable Pedals - the HDM relay was unfused.


At any rate, this forum has helped solve the problem. I don't need DRL's. Can I buy a HDM relay #46 in the aftermarket?
It's a little concerning that one relay doesn't work at all, and the second only works partially - there may be something wrong with your system that will cause a good relay to fail over time.
In any case, the service part number for that solid state relay is 15016745. They're about $20 +s/h from GMPD.

Inko
06-02-2007, 11:31 AM
...I just ordered one from the dealer for $40. sigh...

I just need to deal with this until November when my lease is up.

Thanks Vball and all.

I'll report back once I install the part.

Inko

Inko
06-04-2007, 03:32 PM
One Dealer Mechanic--couldn't solve the problem.
One Auto Mechanic-- couldn't solve the problem.
One TrailVog posting--Problem SOLVED!!!

It was indeed the HDM relay. The reason why the drl's didn't work (initally) was because I wasn't in drive.

Thank you all for your help.

I can just imagine how much the dealer would have charged if I had left the car overnight.

You guys are amazing.

Thanks again,

Inko

808ExT
06-04-2007, 11:59 PM
Ok guys I've got a question for you guys....it seems that since the trailblazer was equiped with DRL my sockets are now burnt to a crisp and the wires look fried also on both sides...but only one side of my headlamps work now and I know it's not the bulb cause the filiment is still good and I used a new bulb just too make sure and yeah it still didn't work....I've checked the relays and yup still good and now it makes me believe it's the socket.

So I came to the conclusion of hmm if I buy a regular 9006 socket from the parts store I could just pick up a HID kit and install it instead of buying the genuine headlamp socket...the only reason why I'm doing this is cause all the parts stores here keep tellin me that they don't carry that socket and that they just sell the regular 9006 straight socket, and that I have to go to the dealer.

What do you guys think will this work, or does anyone have any other suggestions ?

thanks...

paulholcomb
06-05-2007, 06:27 PM
Ok guys I've got a question for you guys....it seems that since the trailblazer was equiped with DRL my sockets are now burnt to a crisp and the wires look fried also on both sides...but only one side of my headlamps work now and I know it's not the bulb cause the filiment is still good and I used a new bulb just too make sure and yeah it still didn't work....I've checked the relays and yup still good and now it makes me believe it's the socket.

So I came to the conclusion of hmm if I buy a regular 9006 socket from the parts store I could just pick up a HID kit and install it instead of buying the genuine headlamp socket...the only reason why I'm doing this is cause all the parts stores here keep tellin me that they don't carry that socket and that they just sell the regular 9006 straight socket, and that I have to go to the dealer.

What do you guys think will this work, or does anyone have any other suggestions ?

thanks...

If you go with an aftermarket HID kit you will actually be cutting wires and hard wiring in the kit.........if you have damage to the OEM components, it's definately worth the swap. However, keep in mind that replacing the different bulbs will cost more and if you don't do it correctly, you will burn up bulbs!!!:yes:

gpdgg
09-28-2007, 08:59 AM
1st post and I have to say thanks for the info. The low beams on my '04 TB just quit last night and I came here and found the answer I needed just like that. Swapped the relays and that was it. In addition I will be ordering the relay from GM direct and saving the dealer mark-up. Thanks again for all the help

mcarter58
09-12-2008, 08:32 AM
I just bought my Envoy about a week ago and discovered the low beams not working yesterday. They worked when I bought the truck--I was also programming a couple of fobs so I wonder if this had anything to do with it. I found the site, found the problem, bought a new relay yesterday from the dealer and my lights work again. I don't want to think what this would have cost if I had taken it to a garage or done the guess and replace method. Thanks guys:D

nidoo
11-09-2008, 02:24 AM
As far as I remember the DRL turned on automatically just when I started my TB 04. Today I noticed that the DRL only turn on when I move the gear selector to a position different than Park (P), and the lights turned off if a put the selector back to the P. This is an expected behavior? The DRL must be turned on all the time?

06gmcenvoy
11-12-2008, 04:21 PM
ya well my headlights still dont work, and the weird thing is my running lights do, just not my low beams... :(

tuggie7
03-15-2010, 07:38 PM
For .me .the .issue .is .not. the .relay's,. I .switched .them .and. it .did .not. work. If .the. problem .is .with .the .BCM .and .I have .to .short the. pink/white. wire. at .pin. A5 .How .do .I .get .a .wiring .schmatic .for .my .TB .so. that .I can .know. what .I am .doing .for .sure?