What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[George B]

Does the temp still show on the DIC?

I've seen that option in the tech2, but I think @Doubeleive might be able to fill you in more on the problem he had and what the symptoms were. Basically I think when its programmed to show the outdoor temp its actually wrong for our model and it will act strange.

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Maybe so on the outdoor temp. I am hoping someone will confirm how their rear HVAC responds to the same settings as mine so I can tell if I have a problem or not. The strange operation existed beforeI changed the outdoor temp display.

The temp does still show on the DIC but I did note other strange behavior in AUTO. I changed it back.
Still hoping for confirmation of “normal” operation. Maybe the program needs to be updated to the current calibration.

 

[Bigkevschopshop]

Looks good! You didn't tell me about your 6.2 Silvy, was it an NHT with 3.73 gears?

6.2 LTZ and 3.73.

 

[gooffeyguy]

The temp does still show on the DIC but I did note other strange behavior in AUTO. I changed it back.
Still hoping for confirmation of “normal” operation. Maybe the program needs to be updated to the current calibration.

I think I remember reading that someone else noticed that the Tech2 controls were backwards when commanding cool or heat.

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[George B]

I think I remember reading that someone else noticed that the Tech2 controls were backwards when commanding cool or heat.

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Might have been me but I thought that too.

 

[Doubeleive]

I haven't messed with mine in a good while but it could be "normal" when you command it hot in the rear that the door moves the opposite, you can take the rear cover off and reach the tech2 back there and observe it while you command it. The rear only has 2 controls up/down and hot/cold and you should be able to command either to 50% and they should be in the middle, then once you see which way they turn for hot/cold you should be able to set the rear for say 75deg and you should see the door move accordingly, if it won't stay on 75 and just goes straight to cold then the head control is not programmed right or one of the roof sensors is goofy. I fought with that thing for good while when I replaced the head control unit in the summer it cooled just fine but when it came winter time it would only heat if set to 100% heat I think it's 90deg, if I set it to 89 it would just go all the way to cold, turned out the head unit had the wrong calibration, before it was reprogrammed it showed the outside temp afterwards it did not and I never messed with it again, I set it to 74 or 76 (auto) and it works great. I don't need to touch it again until it gets hot out.

 

[George B]

I haven't messed with mine in a good while but it could be "normal" when you command it hot in the rear that the door moves the opposite, you can take the rear cover off and reach the tech2 back there and observe it while you command it. The rear only has 2 controls up/down and hot/cold and you should be able to command either to 50% and they should be in the middle, then once you see which way they turn for hot/cold you should be able to set the rear for say 75deg and you should see the door move accordingly, if it won't stay on 75 and just goes straight to cold then the head control is not programmed right or one of the roof sensors is goofy. I fought with that thing for good while when I replaced the head control unit in the summer it cooled just fine but when it came winter time it would only heat if set to 100% heat I think it's 90deg, if I set it to 89 it would just go all the way to cold, turned out the head unit had the wrong calibration, before it was reprogrammed it showed the outside temp afterwards it did not and I never messed with it again, I set it to 74 or 76 (auto) and it works great. I don't need to touch it again until it gets hot out.

How can I tell what calibration is supposed to be in the head control?

 

[Doubeleive]

How can I tell what calibration is supposed to be in the head control?

Goes by your vin number and what it shows on tdsweb, you can connect the tech2 to the vehicle and a computer then open acdelco tds and have it check the calibrations, if there are updates it will show them, tdsweb cost $40 for 2 years programming (per-vin)

 

[Rocket Man]

Goes by your vin number and what it shows on tdsweb, you can connect the tech2 to the vehicle and a computer then open acdelco tds and have it check the calibrations, if there are updates it will show them, tdsweb cost $40 for 2 years programming (per-vin)

That’s what I did after buying a subscription for my Silverado. It showed an update for my hvac control so I though great, I can practice on it before I try programming a new bcm. That’s when I learned about pulling the fuses on any aftermarket electronics because, as I found out, tdsweb attempts to wake up every module and do a handshake to check software versions as it’s programming. And when it couldn’t communicate with my Pioneer HU it got hung up. Which caused programming to stop in the middle of it. I called tech support and we tried everything but no bueno. She finally told me to disconnect the Tech2. The control was bricked, no display and we couldn’t bring it back. I ended up buying a used one from LKQ- a new one was about $250-300. Lesson learned. Pull fuses from any aftermarket electronics before programming.

 

[Fless]

Will your Tech 2 read your current calibrations? You could probably enter your VIN here https://tis2web.service.gm.com/tis2web/ to see the calibration history and availability, and check those against what your scanner tells you is currently being used.

 

[wsteele]

Learned a neat thing today. With my tech2 I was able to set my HVAC display to show the ambient outside temp. Just go to module setup and there is an option to turn it on.

Anyway, need someone with a tech2 to confirm a thing for me. It is about 60* out today and I have my HVAC in auto at 74* with the rear heat HVAC toggled on from the front control. I noted cool air blowing from the upper rear vents. If I increase the system temperature on the main control the air flow from the upper vents decreases and heat blows from the lower vents. All the modes work as they should in manual. Controlling from the front display I can switch to all three modes and increase and decrease temperature as expected in each. The rear HVAC follows the front as expected. Now, the off thing is that on my tech2 when I am commanding the rear air temp door the operation is opposite the command. If I command HOT it gets COLD and vice versus. Does anybody else's act this way? Note, I did replace the rear HVAC control about a year ago with an AC Delco unit from RA.

I just had a minute before I had to come back in and feed the dogs. It was my first time in the body module, so I was just banging around. I can confirm that while the blower seems to correlate with regard to blowing harder as percentages go up, the aux temps seemed to be reversed. My temp goes from 100% at 60F to 22% at 90F. I didn't have time to figure out how to command things from the Tech 2, so that was just display reactions to manual inputs on the rear head.