GMT800 ('04 Suburban) issues - electrical?

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08-19-2019, 10:49 AM
Atrus

GMT800 ('04 Suburban) issues - electrical?

Hey guys -

Asking because I believe a lot of you are familiar with the platform. We picked up a 2004 Suburban in March. 119k on it, very clean from all appearances. Previous owner did mention that he had to replace the 4wd "motor" previously. Not sure if that means the TC actuator, or the front diff actuator. I will look at my documentation from him to see if it's in there.

Everything was fine with the vehicle until last month, and it seems very suspicious that all of this is happening at once. I am starting to wonder if this could be electrical related - ground, PCM/BCM/TCM, something...

Started with a check engine light - P0443 - EVAP Control Valve Circuit. I've replaced both the vent valve (by the tank) and the purge valve (on the manifold). The light still pops up intermittently. It was continual before, but seems like it still goes out of range on occasion.

Next, the "Service 4WD" warning came on - this was a week or two after the P0443. I've checked the grounds under the driver's door area and cleaned them up. I verified that the switch is functional in the dash, and I also verified that the control module is working. Switch and control module were verified by swapping with my 2003 Yukon, which works perfectly - the 'burban parts work perfectly in the Yukon. Still get the error in the Suburban with Yukon parts installed.

The driver's side HVAC temp blend actuator was clicking and seemed bad - I had this happen on my Yukon as well. I honestly don't know if all functions were proper before (HVAC temp and blend settings), but I do know they were at least mostly working as we never noticed an issue. Replaced the driver's actuator, and have attempted to perform the calibration procedure at least 8 times. I've pulled the fuse, I've yanked the battery for a while. I even pulled the control unit for a while and reinstalled it. The passenger side blows warm air, the driver is a mixed bag, and the blend doors function improperly...putting it on "floor"....it'll blow the floor for a few seconds, and then it shifts upward to defrost. Basically, it seems like all 4 actuators are working, but are completely out of sync/calibration.

Any chance you've experienced something similar? Potentially a bad ground? Any thoughts on how to diagnose? I am close to buying a Chinese Tech II clone so I can attempt to diagnose/calibrate and look for any DTC's in the module.
08-19-2019, 05:20 PM
Beigg

T-case fork might be your 4wd issue. Not hard to replace, but it is time consuming as you'll want to pull the t-case out & service it.
The fragile charcoal box tends to break at where the lines connect to it. Look for crack and splits where the lines connect to it.
HVAC control module has been a common fail item from my experiences; knobs interface directly to it. Replacing the unit should resolve those issues.
08-20-2019, 03:05 PM
Atrus

Thanks for the info - I'll look for these items.

Just seemed like a lot of sketchy stuff in a short period. Had me wondering if it were electrical.
08-20-2019, 09:57 PM
Killjoy

If you drop the T-case, make sure you service it, replace the cover, and install the "pump rub" fix. Mine started dripping at ~175k, JB Welded the shit out of it and sold the truck (telling the buyer). If I would've kept the truck, was looking at dropping the TC and overhauling it.
08-21-2019, 07:37 AM
Atrus

I'll have to look into this - had no idea there was an issue with them. I have a Yukon that's creeping up toward 150k, and this thing at roughly 125k, so good to know!
08-22-2019, 06:45 PM
Killjoy

Loved my GMT800, but yea, it's just a matter of time before your Tcase starts dripping.
10-19-2019, 06:56 AM
dline

My silverado keeps staying in 4wd....switc is new, what usually causes this?
10-19-2019, 08:55 AM
capone

Quote:

Originally Posted by dline

My silverado keeps staying in 4wd....switc is new, what usually causes this?

If you replaced the Dash switch it might be Transfecase Encoder Motor.
10-19-2019, 10:30 AM
Atrus

Mine was the encoder sensor on the transfer case
$45 for a new one and all is well.

I highly recommend getting it scanned with a proper TechII type tool. It helped immensely. I actually bought a Chinese clone off Amazon for $120. Runs on a laptop and works like a charm.
10-19-2019, 01:07 PM
CruisnCobra

Quote:

Originally Posted by Atrus

Mine was the encoder sensor on the transfer case
$45 for a new one and all is well.

I highly recommend getting it scanned with a proper TechII type tool. It helped immensely. I actually bought a Chinese clone off Amazon for $120. Runs on a laptop and works like a charm.

Do you have a link for the one you bought? Or are all of the clones basically the same?