Underhood fuse block meltdown, fire near-miss [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Underhood fuse block meltdown, fire near-miss


WhipMeister
07-10-2009, 12:37 PM
Anybody ever have something like this happen?

Daughter borrows my 02 GMC Envoy (which has been a GREAT car - until tonight). She calls about an hour later freaking out (mainly because she averages about $10 of damage per mile when she drives, and she knows it. Black cloud follows that kid around). She says she couldn't get the headlights to shut off and then when she tried to start it, it wouldn't turn over. I'm thinking: Well, it's automatic everything with the lights. Maybe a sensor is bad or something and it killed the battery. But then she says she thinks something is burning under the hood (which is why she's freaking out). She's at a friend's house and he gets on the phone and says he thinks everything is shorting out under the hood (smoke, etc). I ask him if he has a wrench, which he does, and I ask him to jerk the battery cable, which he does. I hop in the other car and get over there. I can smell the ozone stench from 100 feet away.

The underhood fuse/relay/junction box cover is a melted morasse of plastic. I had to work it pretty good just to pry it loose. Under that, this is what I find: :eek:

http://www.lanimation.net/images/envoy.jpg

(took it with the cell camera, so it's not great)

It's a f'ing mess. There's ballast fluid (I guess that's what it is. It like the foul smelling crap in a fluorescent ballast.) all over everything (the brown syrup in the photo). And there are the remains of a couple of relays at "ground zero", pretty much right in the center of the block (the silver blob in the middle of the pic). That's the bad news.

The good *might* be that I checked all the wiring harnesses going in and out of the block and there doesn't seem to be any damage, melted insulation in the harness, etc and they all seem to snap connect into the main block. So I'm hoping that if we replace the block itself and the assorted relays and fuses and bolt it back in we may be ok.

Any ideas? What caused this and why didn't a fuse/breaker/fusible link kill the juice? (It's still pulling serious amps because I accidentally bumped the loose cable back to the terminal while I was fishing around and it stuck). I couldn't find any references to a similar experience out here on the web. I suspect it was the headlight relay at fault, since she said the headlights would not shut off. Anyone know how much that fuse block runs?

Thanks in advance

WOOLUF1952
07-10-2009, 03:40 PM
:tiphat Welcome :tiphat .IIRC, a new/used fuse block is not very expensive. And easy to replace if the harnesses connectors are not melted. Check Parts4Chevys.com, maybe EBay, local salvage yard or, just for s**ts and giggles, a local dealer. I'm sure one of the electrical engineers will be on soon with a theory on the WHY it happened part. I believe a fuse only protects from a short not over heating.

flyingfischer5
07-10-2009, 03:49 PM
:eek:

I've never seen that.

hatchet669
07-10-2009, 04:13 PM
i picked up a front fuse box a littlw while ago... was gunna use it for something else but have decided not to... i'll send ya a text when i get out of work... mite be able to help ya out since i dont need it anymore...

as to why... oh i have no idea... it looks like there was something flammable in/on the fuses and started a fire and just took everything with it... could be outside source.. but i dont know.. do u have any mods to the truck? how many miles? do any major repairs lately?

edit: looking at the pic again.. looks like something shorted or jumped and just over whelmed a relay... i cant tell from the pic what realy that is... but from what u said.. kinda sounds like the power going to the starter went somewhere else... but i'm no EE... roadie will have more insite on this when he gets here im sure... he can smell out electrical problems through the site... lol

WOOLUF1952
07-10-2009, 04:26 PM
That may be a while. The Roadie is incommunicado for a while. And, no, that's not a city in Mexico.:D

WhipMeister
07-10-2009, 04:28 PM
Muchas everyone.

The truck is bone stock. It's been completely trouble free and a joy to own (except for the Alzheimer-afflicted memory mirrors) until this point.

Please do send info on picking up that block from you if it's in good shape and you don't need it.

hatchet669
07-10-2009, 04:30 PM
sometimes he can get on even out in the desert... lol.. he has his ways...

but i wouldnt recomend just throwing in another fuse box... cause if u dont know the problem.. u dont know if its fixed... u may just melt another box and do more damage...

but thinking more bout it... it kinda sounds like the battery/alternator/or starter mite be back feeding power to the fuse box...

Chickenhawk
07-11-2009, 12:32 AM
By any chance, did your daughter try to boost another car? People sometimes use the red and black leads from the fuse block to boost another battery, with instant and disastrous results. (The black wire coming from the fuse block is power, NOT ground.)

Usually the mega-fuse at the fuse block blows, but maybe not in this case. (You should NEVER boost another battery anywhere except directly at the battery terminals.)

I know this is not likely, but I thought I would throw that out there. (By the way, if she DID try to boost someone this way, she wouldn't be the first one ...)

WhipMeister
07-11-2009, 01:00 AM
I'll post the autopsy photos later, but ground zero in the fuse block is around the 45 and 46 'solid state' relays (HDM and FAN). Burned clean through the block and took out a large portion of the connector underneath. I'm guessing the 'solid state' differentiation explains the primordial ooze that coated the whole works and stunk up the shop today.

Googling 'envoy' and 'HDM' reveals a thread of 'known' problems about the headlight relay. Apparently that's what got us. As discussed here:

http://www.justanswer.com/questions/23kd8-2002-gmc-envoy-lowbeams-just-go


The issue now is that I need not only the fuse block, but the center section connector with wires, as the meltdown got into that pretty good too. That would seem to be a salvage yard piece that I will need to splice into the harness after cutting the original away.

Seems to me if this is a somewhat common thing, it might qualify for recall assistance, as the car really could have been ashes today, not to mention my daughter.

WhipMeister
07-11-2009, 01:51 PM
Autopsy photos

http://www.lanimation.net/images/envoy2.jpg

http://www.lanimation.net/images/envoy3.jpg

http://www.lanimation.net/images/envoy4.jpg

Anybody have any possible sources for that connector (with the wires so I can splice it in w/o replacing the harness?)

Thanks in advance

TXBlazer
07-11-2009, 02:09 PM
I would start calling some local boneyards. I'm sure there are a few TV's that are unrepairable that you could cut a harness off of.

the roadie
07-12-2009, 02:35 AM
Got into Portland for a day, but back to the boonies tomorrow. Fascinating carnage. Could have been a lot worse. Too many circuits in this vehicle have constant 12V feeding them with little to stop a meltdown, But this is going to require a junkyard donor vehicle to make it an affordable repair. I'll check the shop manual soon as I can to see if the fusible link should have blown, but after the meltdown starts, there's still 1500-3000 Watts available to melt wires and insulation.

To check GM prices and part numbers, go to www.compnine.com and drill down.

pjaneiro
07-12-2009, 06:20 PM
Before going on to buy another fuse box, that kind of meltdown (enough to melt hard plastics supposed to resist 150 degrees) is not normal, i would start to look at the other connectors like the headlights, the clutch fan and the grounds, also take a good long look at the main wire going from the alternator to the fuse box and battery , if it seems hard and dry, then it's time to change that too, it's easy to say bah, replace the fuse box, and then we hear about a trailblazer on the side of a road on fire with someone stuck inside....

this does not happen normally, yes there is power applied at all times, but still, wire don't catch on fire just for fun, a harsh load or short is needed to vause that carnage , also, if your daughter costs you 10$ per mile, maybe it's time to deny her the permission to use your car, make her buy her own and make her pay for her booboos. it's amazing how people suddenly take care of things they need to work/pay for...

neelskit
07-13-2009, 11:34 AM
I would call the insurance company, take it to the dealer, and let them deal with it. Hopefully they would be able to find the cause of the meltdown.

If it were me, without knowing for sure what caused the short, I would never be comfortable driving (or allowing someone in my family to drive) the vehicle. Too much of a mystery.

However...

The cooling fan solid state relay (#45) is fused at 10A before the relay On the +12V Side. According to the shop schematic, it takes this +12VDC fused connection and open/closes it to the cooling fan clutch solenoid. It is grounded to chassis and is triggered by a PWM signal (most likely 5VDC) from the PCM to control the fan clutch engagement. Since this relay is fused I don't think the short occured here unless it cam from the PCM.

The Low Beam Headlight Relay (#46) is NOT fused before the relay. The Coil of the relay is grounded to chassis and receives a +12VDC signal from the BCM when the headlights are switched on. (This is fused with the BCM) When triggered, it closes a normally open constant +12VDC to two seperate 10A fuses, Fuse 6 and Fuse 3, then to the Left and Right Low Beam Headlights. (Respectively) Now, if the short occured either between the relay output and Fuses 6 & 3, or directly off the normally closed leg of the relay there would have been no fuse to open the circuit to open the short.

Hope this is of use to you...

WhipMeister
07-13-2009, 11:54 AM
I would call the insurance company, take it to the dealer, and let them deal with it. Hopefully they would be able to find the cause of the meltdown.

If it were me, without knowing for sure what caused the short, I would never be comfortable driving (or allowing someone in my family to drive) the vehicle. Too much of a mystery.

However...

The cooling fan solid state relay (#45) is fused at 10A before the relay On the +12V Side. According to the shop schematic, it takes this +12VDC fused connection and open/closes it to the cooling fan clutch solenoid. It is grounded to chassis and is triggered by a PWM signal (most likely 5VDC) from the PCM to control the fan clutch engagement. Since this relay is fused I don't think the short occured here unless it cam from the PCM.

The Low Beam Headlight Relay (#46) is NOT fused before the relay. The Coil of the relay is grounded to chassis and receives a +12VDC signal from the BCM when the headlights are switched on. (This is fused with the BCM) When triggered, it closes a normally open constant +12VDC to two seperate 10A fuses, Fuse 6 and Fuse 3, then to the Left and Right Low Beam Headlights. (Respectively) Now, if the short occured either between the relay output and Fuses 6 & 3, or directly off the normally closed leg of the relay there would have been no fuse to open the circuit to open the short.

Hope this is of use to you...

Thank you. All of that is solid advice and I have a call into the ins co now, although I did order a new fuse block from gmparts direct.

The headlight relay makes sense as the culprit as she said the lights were suddenly stuck on and the starter would not engage before smoke appeared.

neelskit
07-13-2009, 12:07 PM
Let us know what you find out...

WhipMeister
07-13-2009, 12:25 PM
It's covered. $100 deduct. Yay!

exttb
07-14-2009, 08:05 PM
I have a harness from a 2004 I got with my engine swap.....but if your ins covers it...thats great.....intersting since my headlights sometimes dont want to turn on till I restart the car

Frawley03TB4x4
05-21-2012, 10:27 AM
I know this is re: is a few years late, but I have a 2003 TB 4x4 and this past September (2011) About 30-45 minutes after my husband came home from work and the truck was sitting in the yard, this happened to our TB. Noticed smoke coming from under the hood. Grabbed the keys to unlock and by the time we got outside the lights were flashing, doors locking etc. Just about 2 weeks prior to this happening we replaced the low beam Relay on that block. (the one that makes your low lights come on when you engage the trans into drive etc.) I see that your insurance covered this. I tried and mine told me no such luck. What did you tell them to get them to pay for the replacement. My local dealer estimated me around $800 plus as a new fuse block cost $350. Once we pulled the block out one of the connectors was completely melted down and had to be replaced. Talk about a mess!! Since replacing now my service 4 WD light will come on when the vehicle has been running a while or if it is hot outside. If that light comes on my 4wd will not engage, if it's off it will engage and does work. (side note, when the service light comes on my transfer case light still works.) Did you notice any check XYZ lights or anything come on after replacing the fuse block?

WhipMeister
05-21-2012, 11:15 AM
I know this is re: is a few years late, but I have a 2003 TB 4x4 and this past September (2011) About 30-45 minutes after my husband came home from work and the truck was sitting in the yard, this happened to our TB. Noticed smoke coming from under the hood. Grabbed the keys to unlock and by the time we got outside the lights were flashing, doors locking etc. Just about 2 weeks prior to this happening we replaced the low beam Relay on that block. (the one that makes your low lights come on when you engage the trans into drive etc.) I see that your insurance covered this. I tried and mine told me no such luck. What did you tell them to get them to pay for the replacement. My local dealer estimated me around $800 plus as a new fuse block cost $350. Once we pulled the block out one of the connectors was completely melted down and had to be replaced. Talk about a mess!! Since replacing now my service 4 WD light will come on when the vehicle has been running a while or if it is hot outside. If that light comes on my 4wd will not engage, if it's off it will engage and does work. (side note, when the service light comes on my transfer case light still works.) Did you notice any check XYZ lights or anything come on after replacing the fuse block?

Sorry to hear that. I just placed the claim as a 'fire'. I did not try to be very helpful in terms of what I thought the cause was other than my mechanic said it was a fire and I should report it.

They had to manually reconnect every lead to a donor connector. (the alternative is a whole new wiring harness which is major $$$$). It took them a couple of weeks. I definitely could see how there might be one or two connections that might have been missed or not done well. It had to have been tedious as heck. My only lingering issues at this point are 'Service Onstar' and intermittent failure to engage the starter relay (I think that's the switch, though). That and the fact that the stealership that did the work (Jupiter) still owes me $200 since I supplied a brand new fuse block I had purchased before calling the insurance company. They promised and promised to drop it in the mail. Yeah, right. :mad: I think the final tally ended up being about $2400.

My opinion is that this has NHTSA recall written all over it.

George Maser
11-10-2012, 10:33 PM
What was the solution to your problem? George Maser 864-761-7223

jvee85
12-03-2012, 10:12 AM
On 11/15/2012 I replaced the HDM relay #46 on my 2002 Envoy because headlights would not come on. On 12/2/2012 i experienced the meltdown which seems to be concentrated around this relay 46. It is totally burned to a crisp. Had it towed to my regular mechanic shop which is getting to know me and my wallet all too well because of this vehicle.

Anyone have any other info on this problem?

John

tdangle
01-16-2013, 10:34 AM
I just experienced the same thing meltdown of the headlight relay taking out the fuse block. I also had replaced the headlight relay a few months ago. What was the outcome for you that had the meltdown?

WhipMeister
01-16-2013, 01:02 PM
I just experienced the same thing meltdown of the headlight relay taking out the fuse block. I also had replaced the headlight relay a few months ago. What was the outcome for you that had the meltdown?

Insurance replaced it. Ended up about $2k if I remember right. I'm still driving the car.

tdangle
01-17-2013, 01:25 AM
I fixed mine today. I was lucky there was no damage to the connectors and found a like new block complete with all fuses and relays for $125 it took longer to get the part than to replace the block. If I ever have to replace a relay again I will only use GM parts

zaijpaig
01-17-2013, 04:56 AM
See kids..this is what you should do to make a living..
http://www.lsupredent.info/15.jpghttp://www.lsupredent.info/03.jpghttp://www.lsupredent.info/04.jpghttp://www.lsupredent.info/05.jpg

jvee85
01-25-2013, 09:17 AM
My car shop (not a dealer shop) replaced the fuse block and connector with a used parts. On inspection the problem was definitely with the headlight driver relay I replaced a few weeks before the burnout. The bill from my mechanic was $500.

The relay I replaced was bought at a parts dist that distributes parts to most mechanic ships here in our area. But it definitely think the relay was faulty and caused this problem. In the future I will definitely go to a dealer to get replacement relays.

John

Skeith
09-11-2013, 12:06 AM
I have an 03 trailblazer and it just did the same thing. If there is not there should be a recall on this item. Deff a defect in vehicle. If it happens once ok twice we'll maybe but as many people who have posted in this thread. Then I say something stinks in Denmark.

budwich
09-11-2013, 10:35 AM
are you referring to the "non-gm replacement relay" that it appears people are using?

Skeith
09-11-2013, 11:00 AM
are you referring to the "non-gm replacement relay" that it appears people are using?

Your probably referring to the post above mine, but I have not replace a relay as of yet. Have to replace the whole fuse block and who knows what else. I'm going to call gm about this problem will post there response.

rlj0220
10-18-2013, 01:34 PM
Your probably referring to the post above mine, but I have not replace a relay as of yet. Have to replace the whole fuse block and who knows what else. I'm going to call gm about this problem will post there response.


Did you have a chance to call GM regarding this problem? If so, do you mind sharing what they said??

Thank you

jsalinas6
03-06-2014, 06:49 PM
I have a harness from a 2004 I got with my engine swap.....but if your ins covers it...thats great.....intersting since my headlights sometimes dont want to turn on till I restart the car

You wouldn't happen to still have the harness?

Padry
07-08-2014, 09:41 PM
My HDM relay (#46) melted as well, completely fried. I bought this vehicle in January 2013 and the HDM relay looks like the original, but I can't be sure a previous owner didn't replace it. I was able to find a used fuse bock on ebay for $45, but the wire harness connector directly under #46 in somewhat melted. I think the culprit may be an exposed wire connected to the HDM relay. I have some pictures of my ordeal, including the exposed wire, but not sure how to post them in the forum. Let me know if you're interested in seeing them and I can e-mail them.