2005 Trailblazer Rear Hvac Controls

cmccarthy1004

Original poster
Member
Sep 13, 2012
2
Whats up all having a odd issue with my 2005 trailblazer. My rear havc controls are not working, The display is not showing up it is getting power to the rear module. The leds around the knobs are lighting up but the display on the module is not working! I have replaced it and still the same results. If there is any ideas i can try please let me know. Thank y
 

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The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Welcome! Glad you found us.

How are you sure there is power to the module? The lamps are on a dimmable power bus, so they can be adjusted with other interior lamps, and that wiring can light up the lamps without the module itself getting any power.

Do you have a voltmeter and any electrical troubleshooting experience?

Check rear fuse block fuse #39. If it's OK, then pull the module again, and with the ignition on, check voltage at the module's BROWN wire for 12V, and the BLACK wire for a good ground.
 

cmccarthy1004

Original poster
Member
Sep 13, 2012
2
Thank you!
Yes i have the voltmeter, I do have 12volts and a good ground but the one thing i did not check was the fuse! ill go try that and post back with the results
 

CaptainXL

Member
Dec 4, 2011
2,445
Lol. The almighty roadie has an infinite database of electrical circuit diagrams stored in his mind. Or maybe he is just quick flicking through pages of manuals. Bill, the wife is calling you to mow the lawn. "Just a second dear, I need to lookup this fuse at junction block zwith fuse terminal 128 for member joeblow." Amazing:wink:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
CaptainXL said:
..Or maybe he is just quick flicking through pages of manuals. ...
You broke the code. It was critical to read it cover to cover when I first bought it, discover which systems are in which chapter of which of the three books, then discover the GM indexing skill was non-existent (I also wear a tech writer's hat at work) so I know to not bother to look in the index. Then I flagged each of the major chapters to reduce the page flipping, so it really only takes me 30 seconds to look up any schematic in there. And I have a dedicated area of my home office where I keep the manuals available and pre-opened to the chapters that generate the most lookups. Like a human Google cache. :crazy:

Except for front fuseblock #13, which all the regulars have memorized as the accessory outlet fuse that takes out the OBDII function when it blows. :wink:

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