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GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 27664
Experience:  GM Grand Master Technician 2007. 11 years experience.
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Gmc yukon denali: my front blower motor stays on (when the switch is

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i have a gmc yukon denali 2005. my front blower motor stays on (when the switch is off). I have replaced the blower motor. i have replaced the module under the dash. the fan continues to stay on. funny thing is when i put the new module in and tested the circuit (black) ground becomes the line with power &( purple) becomes the ground. When i reinstall the old module purple is hot & black is ground. is there a relay in the fuse box inside of the vehicle ? i also checked the wiring harness as best i could for signs of bad or melted wires..didnt see any problems. i even pulled the control panel from the dash and checked it, no problems...help !
Submitted: 3 years ago.
Category: GM
Expert:  GM Tech (Cam) replied 3 years ago.

GM Tech (Cam) :

Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.

GM Tech (Cam) :

Does this have the auto system with a digital dispaly?

Customer:

yes sir

GM Tech (Cam) :

OK, and you replaced the blower motor controller under the dash?

Customer:

yes sir....when i installed that one black becomes hot and purple becomes ground. with either the new one or the old one installed the blower motor runs when the vehicle is off....i have to end up pulling the fuse under the hood

Customer:

the new one switches the polarity...to be a little clearer

GM Tech (Cam) :

Ok, that is strange as they are common for the failure of this. so next pull the heater control off and unplug it.

Customer:

ok and then what ?

GM Tech (Cam) :

If the motor goes off, then there is a short in the heater control.

Customer:

which plug....the gray side or the blue side ? which side controls what ? also is there a relay in the fuse box inside of the vehicle that could be the issue?

GM Tech (Cam) :

Both of them, you simply want to remove the module from the circuit.

GM Tech (Cam) :

if the display does go out, with the key then I would think the module or wiring.

Customer:

just so i'm following you....pull the ac/heater control out the dash. if the fan stops blowing then the ac/heater control unit may be shorted out.

Customer:

if i wasnt clear before the control unit does go off when the key is removed....the front fan continues to blow only.

GM Tech (Cam) :

Provided the display of the heater is out, yes.

Customer:

ok what if i pull it out and the fan continues to blow...what then ? just trying to cover my bases. i may not be able to find you again lol.

GM Tech (Cam) :

If it still blows then you have a short in the wiring.

GM Tech (Cam) :

As for finding me again, bookmark this page to come back directly to me.

Customer:

cool.....i'm going to give it a shot. will let you know. thanks guy ..God Bless.

GM Tech (Cam) :

Please reply back if you need additional help or press ACCEPT so that the question may be closed out. You can reopen it at any time by replying to it and I will answer ASAP. PLease keep in mind that as experts on this site, we are only compensated for our time spent helping customers once ACCEPT is selected. Thanks again for using Just Answer. Cam.

Customer:

yes sir the fan kept running after the control unit was disconnected....i guess i'm headed to the dealeship..uuggghhh

Customer:

is there anything else i should try ?

GM Tech (Cam) :

I would try cutting the center wire of the blower controller, the small one, simply to 100% eliminate that as the issue, cut it so you can easily splice it back cleanly.

GM Tech (Cam) :

If the motor stays on then you do have another bad blower motor controller, if not then the wiring as we have discussed.

Customer:

the middle small purple wire ? when i tested it with my tester in didnt register power....is that important ?

GM Tech (Cam) :

It is a ground control, so the whole operation revolves around that wire.

Customer:

if cutting that makes the blower stop then what ? if it continues to blow then what ? i'm not going to hold you much longer, just trying to get my leggs under me.

GM Tech (Cam) :

Then the wiring is bad.

GM Tech (Cam) :

If it continues to blow then the controller for the blower there is bad.

Customer:

you mean the module that connects into blower motor itself ?

GM Tech (Cam) :

yes, that is the blower control module.

Customer:

if it stops the wiring is bad...if it continues to blow after its cut then the new module is bad ?

GM Tech (Cam) :

exactly.

Customer:

hey thanks for your time.....i really appreciate your service. thanks again Mr Cam

GM Tech (Cam) :

but only the small wire.

Customer:

got you...only the small wire...thanks again

GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 27664
Experience: GM Grand Master Technician 2007. 11 years experience.
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