2005 Envoy XL SLT Blower Control Module Failure (w/ Auto Climate Control)

WarGawd

Original poster
Member
Sep 2, 2012
468
Per the title, my blower control module seems to have crapped out on me today. Displaying what seems to be the classic symptoms, the fan continues to run at full speed with ignition off/key out/RAP off, and no speed control. Pulled fuse 35 (40A) to shut it off (pulling the 10A fuse and swapping the relay had no effect) until I could get back home and do a little research.

A quick summary of what I've learned (links posted below) is as follows:

  • The FET in the older style modules seem to fail as a result of poor contact with the thermal compound / heatsink. This makes perfect sense in my case, since mine failed pretty much right around the hottest part of the day. At the time, I was only running the fan ~ midspeed, and since my AC also has an as yet undiagnosed leak (and isn't functioning), the heatsink was likely unable to cool the FET sufficiently.
  • The original part has been superceded. GM/AC Delco have an "updated" module that apparently doesn't get along well with older blower motors, requires specific power & ignition switching cycles to work properly, and has a different connector that requires some splicing/adaptation to install.
  • People have found that when using this newer module they were often forced to buy a new blower motor to get proper functionality.
  • The FET can be replaced in the original module, possibly offering opportunities for improving upon the heatsink contact, MUCH CHEAPER (~$6), and saving the hacking and wire splicing.

Relevant threads:


Within those are two specific posts by Roadie (naturally) that are particularly valuable:

This one contains the FET part number(s) - plural because there is a more robust drop-in replacement for the original: http://gmtnation.com/f23/possible-control-module-problem-blower-motor-wont-turn-off-1440/#post44856
And this one contains a series of pictures of the various modules/connector styles: http://gmtnation.com/f23/04-envoy-blower-motor-blower-module-problems-277/#post4149

One piece info that I came across as I looked into this, which may be newer than the posts above, is that apparently there IS another aftermarket module available that solves the problems encountered with older blower motors.

"There was not a software update but another part is now being supplied and so far with no unexpected issues. Click here for the new product link."

This may suit those of you that believe that your blower motor is fine, or aren't comfortable with soldering a new FET on the old control module PCB, for what seems to be a reasonable $77, though you're still left with the connector/splicing issue. In the event you feel like replacing blower and control module, Rockauto has what looks to be a more robust control module by AIRTEX / WELLS for $20 less that may appeal: More Information for AIRTEX / WELLS 4P1516

Lastly, this pic from GM Service Info may help others locate the module for removal (the misspelling of the word 'control' is GM's not mine):

View attachment 29492

For me, I just happen to be heading to Kenny U-Pull in the morning to snag a RR marker light for a Pontiac Wave that got in my way in a parking lot last week :lipsrsealed::mad:....I'll try to pull an old module or two to buy me some time to get the new FET delivered and installed.

Wasn't easy tracking that all down and getting my head around it, hopefully this helps someone down the road.

Cheers, and thanx again to the community at large for putting the info out there.:biggrin:
 

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Mooseman

Moderator
Dec 4, 2011
25,646
Ottawa, ON
The same happened to me except that I had no fan at all. I got a module from an 03 Voy at Kenny U-pull which was a bit different but fit and worked fine. I opened both and my original module had two fets and the 03 had only one. Could have been an updated unit or a replacement. I was lucky this truck was in the Gatineau yard because they are a rare find. For $5, I can't complain :biggrin:
 

WarGawd

Original poster
Member
Sep 2, 2012
468
Mooseman said:
The same happened to me except that I had no fan at all. I got a module from an 03 Voy at Kenny U-pull which was a bit different but fit and worked fine. I opened both and my original module had two fets and the 03 had only one. Could have been an updated unit or a replacement. I was lucky this truck was in the Gatineau yard because they are a rare find. For $5, I can't complain :biggrin:


I have to go anyway, to get the marker light for the other vehicle, but being in Smiths Falls, I was just heading to the Ottawa location - any wild guesses as to my odds of finding a control module there?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
One of my current projects is stress testing of power FETs, and I'm amazed how much better the new ones are than the old ones. Cheaper, and about 90% cooler running than the ones I looked into years ago in these modules. If I was designing this unit today, I'd use a $1 FET that is only 5mmX6mmX2mm thick that you can barely see to solder down. I suspect it wouldn't even need a heat sink, it's so efficient. Used as an on/off switch, I've measured more dissipation (waste heat) coming out of many mechanical relays than this new generation of FET.

Here's one for a quick analysis: Infineon BSC100N06LS3 G. 60V breakdown voltage. 50A continuous current. 200A peak pulse current. 10 milliOhm max on-resistance. At the typical motor draw of 20A DC on high speed (worst case for the switch), let's say, the RDS(on) is 8 milliOhms, so that's 160mV drop across the device, or around 3 Watts. 5mmX6mm package. Capable of dissipating 50W if you solder it to a heat sink or a large copper plane on your PCB. $1.05 at Digikey.

For the same TO220 FET package style as they use now, you could buy a $3 International Rectifier IRFB3256PBF, with 3.5 milliOhm resistance at 75A. That would dissipate 1.4 Watts at 20A in a package that can withstand 300 Watts with a good heat sink. Safety margin up the wazoo!
 

dazingla

Member
Jul 14, 2013
102
Mooseman said:
The same happened to me except that I had no fan at all. I got a module from an 03 Voy at Kenny U-pull which was a bit different but fit and worked fine. I opened both and my original module had two fets and the 03 had only one. Could have been an updated unit or a replacement. I was lucky this truck was in the Gatineau yard because they are a rare find. For $5, I can't complain :biggrin:

the one off merivale has 2 envoys right now. so if u need anything id go now lol .
 

Mooseman

Moderator
Dec 4, 2011
25,646
Ottawa, ON
the roadie said:
One of my current projects is stress testing of power FETs, and I'm amazed how much better the new ones are than the old ones. Cheaper, and about 90% cooler running than the ones I looked into years ago in these modules. If I was designing this unit today, I'd use a $1 FET that is only 5mmX6mmX2mm thick that you can barely see to solder down. I suspect it wouldn't even need a heat sink, it's so efficient. Used as an on/off switch, I've measured more dissipation (waste heat) coming out of many mechanical relays than this new generation of FET.

Here's one for a quick analysis: Infineon BSC100N06LS3 G. 60V breakdown voltage. 50A continuous current. 200A peak pulse current. 10 milliOhm max on-resistance. At the typical motor draw of 20A DC on high speed (worst case for the switch), let's say, the RDS(on) is 8 milliOhms, so that's 160mV drop across the device, or around 3 Watts. 5mmX6mm package. Capable of dissipating 50W if you solder it to a heat sink or a large copper plane on your PCB. $1.05 at Digikey.

For the same TO220 FET package style as they use now, you could buy a $3 International Rectifier IRFB3256PBF, with 3.5 milliOhm resistance at 75A. That would dissipate 1.4 Watts at 20A in a package that can withstand 300 Watts with a good heat sink. Safety margin up the wazoo!

What he said :biggrin:
 

WarGawd

Original poster
Member
Sep 2, 2012
468
dazingla said:
the one off merivale has 2 envoys right now. so if u need anything id go now lol .

Got there this morning, as it turns out there was only one - an '02 LWB. Managed to scavenge a Cabin Air filter door, a blower control module, drivers side window switch assembly, rear wiper motor, liftgate module, and a liftgate glass with perfect defrost grid, all for $65!! For an '02, it seemed to be in decent shape except for the front end damage that likely killed it in the end - with 351k km (218k mi) on the odometer!

Ran into Mooseman there too. After 2-1/2 hrs in the heat, I was dying. Thanx for the extra hand at the end Moose ;-)
 

dazingla

Member
Jul 14, 2013
102
WarGawd said:
Got there this morning, as it turns out there was only one - an '02 LWB. Managed to scavenge a Cabin Air filter door, a blower control module, drivers side window switch assembly, rear wiper motor, liftgate module, and a liftgate glass with perfect defrost grid, all for $65!! For an '02, it seemed to be in decent shape except for the front end damage that likely killed it in the end - with 351k km (218k mi) on the odometer!

Ran into Mooseman there too. After 2-1/2 hrs in the heat, I was dying. Thanx for the extra hand at the end Moose ;-)

yeah thats the gold one with 350 on it. there was also a silver one in the very back row next to two red montanas. Maybe it was to scraped so they crushed it. the one in gatineau has a regular envoy but its been there awhile. the website says its a recent arrival but its been there for about 6 months!!!.
 

Mooseman

Moderator
Dec 4, 2011
25,646
Ottawa, ON
Yep, was good we ran into each other. You were definitely out of gas and I was happy to help out. I only needed a couple of little things but may go back for more when this heat goes away. My G80 is borked, acting like a regular open diff so I may grab the carrier.

I go there on a regular basis and haven't seen any others at all. The back two rows were cleaned out. The gold one is fairly fresh and still has a lot left. The blue one in Gatineau is also an XL and has been stripped pretty much clean except for the engine itself. It's been there since May so is likely to go soon.
 

dazingla

Member
Jul 14, 2013
102
If were lucky they will get my 02 envoy SLT Frame on it was bent so insurance company wrote it off. I was gonna buy it back but then i would only be getting 1500 bucks back!!!! said **** it and just get another.


View attachment 29529
 

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WarGawd

Original poster
Member
Sep 2, 2012
468
Turns out Mooseman may have snagged the correct replacement blower module for my '05, and vice versa. Attached some pics for him and other to see:

The part I snagged from the '02 Voy, PN 52494707

View attachment 29531

View attachment 29533

Comparison of the two:

View attachment 29535

And a closer view of the 2nd gen version for MY '03-'06 (I believe) PN 52409643 (251946786):

View attachment 29536

Moose may be having problems using v2 in his '02 TB, for the same reason that later model years have issues with the 3rd version...not sure. But we can swap 'em and see :smile:

Cheers
 

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WarGawd

Original poster
Member
Sep 2, 2012
468
BTW, although it may appear those tabs on my old module simply depress to allow one to remove the cover to access the PCB for replacing the FET, it doesn't seem like it. Not sure how to crack the case on this one, if anyone has any input, fire away :smile:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
If the tabs don't depress, the cover can be expanded by a thin flat blade to get over them. Or break 'em. Weld the cover back on with a soldering iron. JB Weld. Duct tape. Only somebody with OCD really cares if the factory tabs are all intact on every module and connector in the vehicle. :wootwoot:
 

WarGawd

Original poster
Member
Sep 2, 2012
468
the roadie said:
If the tabs don't depress, the cover can be expanded by a thin flat blade to get over them. Or break 'em. Weld the cover back on with a soldering iron. JB Weld. Duct tape. Only somebody with OCD really cares if the factory tabs are all intact on every module and connector in the vehicle. :wootwoot:

That's the trouble - the cover seems to be extremely well attached to the heatsink base - I only tried briefly while trying to snap the above pics, but I couldn't get a flathead screwdriver, even a small precision variety, to make any headway depressing tabs, or separating cover from base....thought there might be a trick I was overlooking.
 

Mooseman

Moderator
Dec 4, 2011
25,646
Ottawa, ON
There's a screw under the label. You should feel the depression, I think right under the (2p).

Mine is acting bizarre. First thing in the morning, no problem. Then if I stop and start it up again, it won't start blowing again until I start moving again. And it's been getting worse. Today, I had to go at 100 Km/h to get it going again, before it was 50/60/70 Km/h. It's as if the fan is getting stiff and needs a bit of wind to get going. I'd have to do some tests to see if power is getting to the motor. Otherwise, it's back to Kenny's. Unfortunately, I am in the middle of my work shifts and won't be free until next Friday. I might try to test it tonight.
 

Mooseman

Moderator
Dec 4, 2011
25,646
Ottawa, ON
It's my blower motor. Took the kick panel out and the motor wouldn't spin. Tapped it and it got going. Took it out, cleaned the rotor brush contacts through the vent hole and oiled the bearing. Slapped 'er back in, works. I even tried my original module, also works so it was the motor the whole time. Time will tell if my quickie repair job will work but left the kick panel out in case I need to kick it again but I will go and get the other motor from the yard.

Wargawd, I'll PM you so we can organize a swap sometime.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
Mooseman said:
It's my blower motor. Took the kick panel out and the motor wouldn't spin. Tapped it and it got going. Took it out, cleaned the rotor brush contacts through the vent hole and oiled the bearing. Slapped 'er back in, works. I even tried my original module, also works so it was the motor the whole time. Time will tell if my quickie repair job will work but left the kick panel out in case I need to kick it again but I will go and get the other motor from the yard.

Wargawd, I'll PM you so we can organize a swap sometime.

That's not why I thought it was called a kick panel. Who knew? :rotfl:
 

WarGawd

Original poster
Member
Sep 2, 2012
468
Mooseman said:
There's a screw under the label. You should feel the depression, I think right under the (2p).

BINGO! That's the trick I was missing. And it looks to me like the contact between heatsink and FET was actually pretty good in this case:

View attachment 29698

View attachment 29700


Mooseman said:
It's my blower motor. Took the kick panel out and the motor wouldn't spin. Tapped it and it got going. Took it out, cleaned the rotor brush contacts through the vent hole and oiled the bearing. Slapped 'er back in, works. I even tried my original module, also works so it was the motor the whole time. Time will tell if my quickie repair job will work but left the kick panel out in case I need to kick it again but I will go and get the other motor from the yard.

Wargawd, I'll PM you so we can organize a swap sometime.

Yep - that should give you your original module and an identical backup that so far has given me zero issues over 100+ ignition cycles with various fan states. And the one you got to replace the one you thought failed must be a match for my '05 - so when I order the FETs, I'll have the same situation. Works for me :biggrin:
 

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