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roybelding
roybelding, Master Tech/Trainer
Category: GMC
Satisfied Customers: 5446
Experience:  35 years of retail operations on all vehicles
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2003 GMC Yukon XL rear blower not operating. There is 12V

Customer Question

2003 GMC Yukon XL rear blower not operating. There is 12V coming into the blower resister but only 3-4V coming out. There is also a tiny purple input wire going into the resister and I don't know how to get a reading on that to ensure the system is even feeding the rear to turn on.
Submitted: 7 months ago.
Category: GMC
Expert:  roybelding replied 7 months ago.

good morning my name is ***** ***** I will assist

let me get a wiring diagram for you

Roy

Expert:  roybelding replied 7 months ago.

ok check the diagram I sent you and verify the 2 fuses listed have 12 volts on each side.

you said the output was low??? which wire did you measure???

Roy

Customer: replied 7 months ago.
Fuses are good. Voltage equal on both sides of fuses.I check power input on the Orange wire in the back coming into the resister. It's 12V. Purple wire coming out of resister to blower is 3-4v. There is also a tiny purple input wire to the resister and maybe that's an issue?What's weird about the controls in the front is that I set the roof to AUX and hit the Power on the rear seat controls and it will only read OFF
Expert:  roybelding replied 7 months ago.

ok, what about the brown wire???

seat controls??? I thought we have an issue with the rear blower???

Customer: replied 7 months ago.
The climate controls in the rear seating area. Sorry for not clarifying.Not seeing any brown wire in the back at the motor.
Expert:  roybelding replied 7 months ago.

this is an input wire to the resistor. not at motor.

Expert:  roybelding replied 7 months ago.

sorry, I sent you manual control.

check this one

Expert:  roybelding replied 7 months ago.

is there any voltage on the ppl wire from the module to the resistor???

Roy

Customer: replied 7 months ago.
No voltage on purple wire at all. And I have the blower switch in over head climate controls in the front
Customer: replied 7 months ago.
The temperature actuator is making all kind of noise in the back too. I assume because the blower isn't operating. Maybe it trying to adjust
Expert:  roybelding replied 7 months ago.

it is pointing to the hvac control module in the rear. that get a signal from the front from a serial line.

do you have a scan tool to monitor the ac controls???

no, the noise comes from the plastic gears in the motor failing. that will need to be replaced as well.

Roy

Customer: replied 7 months ago.
What scan tool do I need? I have an OBDC2 tool only here.I have the very front over head climate control fan knob cranked to full speed. That purple wire in the back at the resister has .01V. Basically no voltage coming back.
Expert:  roybelding replied 7 months ago.

you need a full blown scan tool, not a code reader.

serial lines carry very low voltage. it is not something you measure with a volt meter

Roy

Customer: replied 7 months ago.
this is the rear control module I see under the fan with 3 connectors that could be the issue? Not any switches up front?
Expert:  roybelding replied 7 months ago.

you have power into the resistor from the fuses.

thats why you need a scan tool to see if the signal is getting back to the module. in most coses, it is the module that is the failure as that controls the fan speeds through the resistor

Roy

Customer: replied 7 months ago.
there is power coming into the resister. When I take the power coming into the resister and jump it straight to the blower is spins.I don't want to dump thousands into this but I just bought this vehicle for family road trips. Rear climate would be nice to have. Should I take it to the dealership? Anywhere to rent the scan tool? Just replace the module?
Customer: replied 7 months ago.
The module I'm seeing back here is for the electronic suspension. So I'm not sure where the AC control module is located.
Expert:  roybelding replied 7 months ago.

no one rents a full scan tool. they cost about 3 to 5k.

you could at least have someone look at it and finish the diag and confirm the module. at least you will know and then you could complete the repair to save money. it would be ell worth the 150 for the diag.

let me see if I can find a picture

Roy

Customer: replied 7 months ago.
I found it. Sorry. It's half way up the system. Dude I'm super obsessive and knowing something isn't working will eat me alive! haha. The module is $67 on Amazon. In your expert opinion should I start by replacing that?
Expert:  roybelding replied 7 months ago.

good, glad you found it

I feel confident based on your info that is the issue

Roy

Expert:  roybelding replied 7 months ago.

please dont forget to rate me as it is the only way I get paid for my efforts

Roy

Customer: replied 7 months ago.
Would the control module prevent the rear seat controls from coming on?
Expert:  roybelding replied 7 months ago.

no

Customer: replied 7 months ago.
Then why is the rear seat climate controls constantly saying OFF even if I press the power button?Upon looking up the rear AC control module I found a TSB that says this happens and over adjusts the actuators causing a fault.
Expert:  roybelding replied 7 months ago.

thats another reason you need a scan tool to monitor the controls as I stated before.

when the module in the rear turns on, then it will say on. that signal comes from the rear module

Roy

Customer: replied 7 months ago.
Wel holy shit I reset the vehicle and now the rear controls come on. Someone posted in the reviews how to recalibrate the system. Everything is working as the Amazon review for the part described. Insane.
Expert:  roybelding replied 7 months ago.

ok, thats good. the question is, why did it not work. re setting is not a repair at all. if it went out once, it will continue until there is no more re setting

Customer: replied 7 months ago.
The ticking actuator is going over its limit and causing a fault in the control module which is then shutting it all down. When I remove all power to the module for a few minutes it's resets itself. I'm sure the actuator will send another fault and trip the whole thing. I'm going to replace that actuator.
Expert:  roybelding replied 7 months ago.

the actuator will not shut down the module. there are stops on the mode door. when the motor hits them, that is what causes the plastic gears to fail. very common failure

Customer: replied 7 months ago.
I opened the actuator and all the teeth were perfect. I reset the nail gear that controls the door so it lined up to the indicators on the actuator cover. Put it all back together and it works perfect. When I flip to heat I watch the actuator and it closes the door from cold and it blows hot. When I turn to cold I see the doors change again. It was really that Amazon review that got me there, sorry man

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