Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

03 TB Ext Rear A/C - Radio No Power

16K views 32 replies 8 participants last post by  RuffRyder2008 
#1 ·
The rear a/c - radio on my center console has no power to it, and you can't turn on ac or heat from the switch by the shifter either. I have checked the fuses under the rear seat and all look fine. Any ideas on what else to do? Thanks...
 
#2 ·
The front switch for the rear unit is powered by the AUX HVAC control mod. It's powered from fuse 36 in the rear fuse box. But the radio controls are separate, as far as I know. Do u have any lights working on these controls? If no, look for a disconnected cable near/under the console.
 
#4 ·
I think it comes out with out a lot of work. You need to remove the shifter handle (small screw under thumb button) and if these are like other GMs, the shifter need to be in the vertical (like in D). After removing the cup holder liners and the insert under the cover, the screws should be visible.
 
#8 ·
Not a fuse

Thanks for the suggestion but I had already checked the front and rear fuse panels. Relay 45 for the rear fog lamps seems to be missing. Is this possibly related?

It is a used vehicle which I found had a leaking rear heater core. The theory is that the seller might have disabled the rear system somehow.

Any other thoughts?

John
 
#9 ·
Thanks for the suggestion but I had already checked the front and rear fuse panels.
Wish you had added that to your first post. Helps us understand better what level of suggestions to suggest. You might not believe it, but we've had some newbs show up here not ever reading the owner's manual, not knowing they even HAD a rear fuse panel. :rolleyes:
Relay 45 for the rear fog lamps seems to be missing. Is this possibly related?
Wish you had filled out your profile with location. I may be wrong, but I think rear fog lamps aren't an option for US vehicles. We have backup lights, but they are in different locations for Envoys versus TBs. Maybe you're out of the US? Anyway, the rear fog lamp option, if you have it, is RPO code T79 on the glove box sticker. And the relay isn't at all connected to circuits for the rear audio or HVAC controls.
It is a used vehicle which I found had a leaking rear heater core. The theory is that the seller might have disabled the rear system somehow.
Wish you had filled out your profile with what vehicle you have. (See the trend here? :D) I thought you were a short wheelbase (SWB). The long wheelbase vehicles, as you said, have a rear heater core. If it was leaking, the previous owner may well have disabled the control to make sure the coolant bypass valve doesn't even send coolant back there to leak. I've even seen folks fiddle with hoses to make sure no coolant gets sent to a leaking core.

If the fuses are OK, then the previous owner probably pulled the connector off the back of the rear control module/display. Have you been inside the console to check it out? You have to remove the shift handle with a Torx driver, plus a bunch of other hidden screws, to take out the console.
 
#13 ·
Thanks again for the pointers however all is well within the console - no disconnected wires and the power/cigarette lighter in the console works.

More puzzling, or maybe the key, is that the R/0/1/2/3 switch also does nothing. So to recap, everything in the console is dead (R/0/1/2/3 switch, rear stereo controls, and rear Heat/AC) except the cigarette lighter. Any other suggestions?

Is there a computer or a board somewhere that controls this? I also saw references to several service bulletins that may be related to this but I do not have access to the bulletin details. They are: 020139003, 020139003A, & 040845010.

It is a US long wheelbase model, XL, SLT with just about all options but the DVD system. Thanks.
 
#14 ·
More puzzling, or maybe the key, is that the R/0/1/2/3 switch also does nothing. So to recap, everything in the console is dead (R/0/1/2/3 switch, rear stereo controls, and rear Heat/AC) except the cigarette lighter. Any other suggestions?

Is there a computer or a board somewhere that controls this?
As you probably know, the R/0/1/2/3 switch is for the driver to control the rear HVAC. When in the R position, the control is passed to the controls on the rear of the console. The 1/2/3 are fan speeds. The 0 (zero) is actually an O for OFF. When in this O position, the rear HVAC will not run.
You might have a bad switch.

The switch (above) has only 2 wires (plus the light), they both go to the rear HVAC control module (I think it's under the plastic panel at the rear of the truck, behind the rear passenger side door, where the rear fan vent is located). The rear passenger controls also connect to the rear HVAC control module. You might have a bad Rear HVACCM.

The rear HCACCM is powered from the HVAC-B fuse in the rear fuse panel, but this has been checked.

Try a new R/O/1/2/3 switch, it's the cheapest component.

PS, this does not address the rear stereo controls. If they are not working because of the same problem (and you don't know this), then all of the above can be tossed.

If one problem is causing all of the problems, they might be an open ground in the console area (just a guess).
 
#21 ·
I don't see any relay that deals with the rear blower. It's all fuses. The only relay I see in a quick scan of the HVAC schematics is in the front underhood fuse block, relay 44, for the AC compressor.

Can you see if there's 12V on the orange wire going into the control module? If that was gone, even if the HVAC-B fuse was OK, it would explain a lot.

And what about our question about the lights in the rear console?
 
#24 ·
No, the orange just brings 12V from the fuse block. It shows continuity to where?

12V comes from HVAC-B fuse 36 through connector C307 (hidden in the console) to the control module input connector (two rows of sixteen pins)

By control module, I just meant the box in the rear of the console where the HVAC and audio buttons are.

I bet there's a problem with C307 and to get to that you need to remove the console.

The power receptacle comes from a different path.
 
#26 ·
A couple of posts ago, you said there was no power on the Orange, but it has it now? Just checking.

Sorry. I should have just scanned and posted this schematic earlier.

The module is at the bottom. If Orange has power, and black has ground, then check yellow on B11. The R/0/1/2/3 has as its input the "low reference" signal, which is zero volts. When the switch is on R, the yellow wire should be at ground.

But you have too many things not working for it to be the R/0/1/2/3 switch only. Such as the audio display not working.

The 5V reference for all the mode and temp actuators comes from the control module. See if Pin A13 (gray) has 5V on it.

The lights are lighting up because they get their dimmable power from a different path, not shown on this schematic. But since they work for you, it's pretty sure you have a good ground.

Although that isn't always a good indication because lights don't present a lot of load, so a corroded ground may still work for lamps but not for motors. But the clear indication that this is happening - not for this troubleshooting exercise but just as a heads up for the future - if that kind of ground corrosion is suspected, a control module's lamps may work fine, but when a larger load like a motor is commanded, the motor will fail to work and the lights will ALSO go out or dim.

So if you have a good power and ground, see if you can find a buddy with the same vehicle to trade modules with for a minute. Don't suppose you're close to San Diego, eh? :undecided
 

Attachments

#28 ·
Part number for rear AC/radio control

Thanks for all of your previous help. I am just now getting back to troubleshooting my rear stereo/AC control issue since it is getting pretty warm now in the NE. Do you by any chance have the part number available for the rear control unit (the display and buttons in the rear of the console)?

My local mechanic, who owes me a fix after I spent so many troubleshooting $ with him, says that my VIN (when read over teh phone to the dealer parts counter) doesn't indicate that I have the rear AC unit so no part is coming up.

John
 
#29 ·
My 2002 Envoy's rear audio/HVAC took a crap, I replaced it with a unit from a 2005 Envoy. The buttons were different looking and it was obviously newer, I was concerned it wouldnt work but alas it was plug and play and now I have my rear radio and a/c back! :cool:

Just find one that is working and swap. I was able to get mine on ebay for $9.99. I was the only bidder :thumbsup:
 
#31 · (Edited)
bad control module?

I am having the same problem on a 2002 TB. Checked the harness under the center "glovebox" and it is all connected but neither the rear radio or rear heating/ac controls have a display. The buttons do light up and the lighter works. Was it ever diagnosed to be a bad control module?

Also, my wiring diagram is different and had an A and B side that have numbers going up to only 9.

The next may seem like a stupid question but am I supposed to have a rear control knob somewhere on my dash? Its a new truck and I really don't have a clue if it is supposed to have one...

Thanks!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top