Question about 2003 GMC Yukon Denali

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GMC Yukon Denali XL Auxiliary Blower Motor Battery Drain

I have been stumped on this issue for weeks on my 2003 GMC Yukon XL Denali (Automatic climate control). It started because the battery would drain after letting the truck sit overnight. I would go out in the morning, and battery was dead. Long story short, took it into the dealer to diagnose and he traced it to the auxiliary blower motor running when the car was off. I tore apart the rear trim to get to the auxiliary blower motor and sure enough, it ran on very low speed when the truck was off. When the truck was on, it would function at all speeds.

The dealer tech was going to replace the auxiliary blower motor module (resistor type thing), so I decided to do it myself. I ordered the new part in from GM Parts Direct and plugged it in. The new module blows on full speed with the truck off. When the truck is on, the fan speed cannot be controlled, it is only on full speed. When I plugged the old module back in, it worked fine when the truck was on, but still was running the blower on very low speed with the truck off.

Where else in the system could there be an issue? If the module isn't the issue, why are they acting differently?

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  • erikgbergers May 18, 2010

    So, I hooked up the voltmeter to the plug that goes into the resistor and everything upstream was functioning properly. No voltage when the truck was off or the blower was set to off. It increased as the blower setting was increased. This was having the black lead on the ground and the red lead on the control. It was a constant 12V when red was on power. I'm not an electrical expert, so sorry if that is obvious.

    When hooked up to the plug going from the resistor into the blower motor, the old resistor works fine, but is still sending voltage when the truck is off. The new resistor is always sending max voltage and does not change when the truck is off or with changing the blower dial.

    Am I wrong in assuming everything upstream is functioning properly? I am wondering if the new resistor I got from the dealer is bad. Any thoughts?



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Could be that the switch itself is shorting and allowing power to flow,if you can get to the switch I would use a voltmeter and see if there is voltage on the output side with the switch off.

Posted on May 14, 2010

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Your new resistor should contain a built in relay. Sounds like that is sticking, swap the new part for another as it could be that you got a bummed replacement.

Posted on Jun 04, 2010


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