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Instrument panel lights all on at once

Tiny
90SIERRA
  • MEMBER
  • 1990 GMC SIERRA
  • 5.7L
  • V8
  • 2WD
  • MANUAL
  • 180,000 MILES
Just bought the truck listed above 1500. The blower fan was apparently getting stuck. Sometimes it would work Sometimes it wouldn’t. Usually it would stay stuck on one of the 3 positions-High, Med, or Low and not shut off. My husband replaced this whole module, and now the whole display lights up all at once. You can’t select anything, it just stays lit up.
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Wednesday, August 26th, 2020 AT 5:39 AM

10 Replies

Tiny
4DRTOM
  • MECHANIC
  • 467 POSTS
Hello,

Interesting, sounds to me like the new one put in is faulty. Was it purchased new or used? You can try to do a reset on it though by disconnecting the both battery terminals and shorting the two cables together for 30 seconds this will reset the system. Give that a shot and let me know what happens and we can go from there.
Tom
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Wednesday, August 26th, 2020 AT 4:50 PM
Tiny
90SIERRA
  • MEMBER
  • 5 POSTS
The module we bought was used and sold in “good working condition”. Couldn’t find new ones available for sale.
We will try your suggestion, thanks so much for taking the time to answer!
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Wednesday, August 26th, 2020 AT 9:02 PM
Tiny
4DRTOM
  • MECHANIC
  • 467 POSTS
Hello,

Sure thing, hopefully it will work but you always have to be careful with used electronics there is no real way to tell if they are good until you install them and they can be damaged in either shipping or when It was removed from its original home.
In view A in the upload below there is the control for the heat, is this the part you bought? If it is doing the battery thing wont deal with it.
Are the fans turning on and the system is working and just the display is haywire or is it not turning on?
Let me know,
Tom
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Friday, August 28th, 2020 AT 11:08 PM
Tiny
90SIERRA
  • MEMBER
  • 5 POSTS
Tom,

That looks like the part we replaced. We haven’t tried the reset with the battery cables yet. We should have time this weekend to work on the truck. We were going to pull the module back out and inspect the wiring and plug and try the reset.

The fan does turn on. And you can change where the air exists the vents- floor, dash, defrost. It appears to blow hot air all of the time but our weather has been nearing the 100 deg range, so it’s hard to tell if it is the outside air temperature or actually producing heat. The A/C wasn’t working when I bought the truck and hadn’t been working for several years. Right after I bought it and before we replaced this module, I had our mechanic diagnose some problems for me. He determined we need a new compressor kit and condenser. We were going to order we these parts this weekend.
A couple times this week, the display has gone dark. So it went from everything lit up to nothing at all. I will check it later and see if it lights back up when I start it. It was unlit all day yesterday, I probably turned the vehicle on and off a half dozen times over the course of the day. Thanks for your help!
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Saturday, August 29th, 2020 AT 4:47 AM
Tiny
4DRTOM
  • MECHANIC
  • 467 POSTS
Hello,

All off, there might be a bad connection right at the plug. When you do take it apart again look into both the male and female sides of the plug for corrosion or debris of any kind.
Keep me posted.

Tom
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Saturday, August 29th, 2020 AT 8:47 PM
Tiny
90SIERRA
  • MEMBER
  • 5 POSTS
My husband took the part out this weekend. We did not see any corrosion or debris on either end. Just so happens we have an inoperable Chevy of similar vintage. He installed the module from the Chevy and it works without any problems so far. So we didn't determine what was wrong with the module we bought, but we have working controls now. Thank you for your help!
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Wednesday, September 9th, 2020 AT 9:32 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I'm Danny.

Just to add my 2 cents. Something you might want to consider is upgrading your A/C system from R12 to R134a. I converted my 1989 Silverado and the cooling difference is spectacular being an extra cab to cool off. The upgrade only cost $300.00 and took about 3 hours at my local A/C shop. Hope this helps and thanks again for using 2CarPros.
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Wednesday, September 9th, 2020 AT 12:27 PM
Tiny
90SIERRA
  • MEMBER
  • 5 POSTS
Thanks Danny, I will look into that.
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Wednesday, September 9th, 2020 AT 12:57 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
You're welcome!
Thanks again for using 2CarPros and we hope you will use our site again in the the future.

Danny-
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Wednesday, September 9th, 2020 AT 2:25 PM
Tiny
4DRTOM
  • MECHANIC
  • 467 POSTS
Hi,

I'm glad it all worked out and your doing fine now.
If anything else comes up be sure to come back. Be sure to tell any friends that might need assistance, we are here to help.
Tom
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Thursday, September 10th, 2020 AT 9:59 PM

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