Battery Drain From Auxiliary Blower Motor? Stumped

bergersen · May 14, 2010

I have been stumped on this issue for weeks on my 2003 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? I am lost in this issue and could use some guidance. Thanks much. Sorry for the long writeup, I'm usually a searcher, but have found nothing on this issue.

bossier62guy · May 14, 2010

I have been stumped on this issue for weeks on my 2003 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? I am lost in this issue and could use some guidance. Thanks much. Sorry for the long writeup, I'm usually a searcher, but have found nothing on this issue.

Did the electrical plug look ok? I know the plug for the resistor up front can get too hot and melt causing a similar issue but I'm not sure about your situation....just a thought.

bergersen · May 18, 2010

I checked the plug and it looked okay. Thanks for the thought. I know what you're talking about. That happened to the front blower motor of my 99 Silverado.

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?

bossier62guy · May 18, 2010

I checked the plug and it looked okay. Thanks for the thought. I know what you're talking about. That happened to the front blower motor of my 99 Silverado.

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?

I've only got a Chilton's that covers 99-02 in my hands at this time and the wiring diagrams leave a little to be desired. I do have the factory shop manuals but I'm in the process of relocating and they are packed up in storage at this time....your 03 might be a little different anyway but....from what I can see the only way you're getting full blower operation w/ the system off is if the blower motor relay is malfunctioning. What fuse will kill the blower? Is it a 30A fuse in the underhood electrical center?

gmtech4 · May 18, 2010

the module is not the resistor so I'm confused ,if it is a module you cannot just plug it in,it has to programed first . but hey I've been wrong before .I have no access to GM info anymore.

what about the aux control head (which is a module up front)if that is unpluged while the blower is running KOEO(key off engine off)does it shut off?

i know ,clear as mud lol

if someone here can look it up in GM SI ,they could tell if it needs to be programmed.

it running half speed maybe a default thing

bossier62guy · May 18, 2010

the module is not the resistor so I'm confused ,if it is a module you cannot just plug it in,it has to programed first . but hey I've been wrong before .I have no access to GM info anymore.

what about the aux control head (which is a module up front)if that is unpluged while the blower is running KOEO(key off engine off)does it shut off?

i know ,clear as mud lol

if someone here can look it up in GM SI ,they could tell if it needs to be programmed.

it running half speed maybe a default thing

Robert, that's why I asked him what fuse would stop the motor. I'm thinking it might not be running at full speed and he could indeed have a faulty control module. I am assuming that he does have the overhead module controlling the rear air???

bergersen · May 19, 2010

I've only got a Chilton's that covers 99-02 in my hands at this time and the wiring diagrams leave a little to be desired. I do have the factory shop manuals but I'm in the process of relocating and they are packed up in storage at this time....your 03 might be a little different anyway but....from what I can see the only way you're getting full blower operation w/ the system off is if the blower motor relay is malfunctioning. What fuse will kill the blower? Is it a 30A fuse in the underhood electrical center?

Yes, The blower does not function when the RR HVAC fuse from the underhood box is pulled. It is a 30A fuse.

bergersen · May 19, 2010

This is the part that I ordered in. It is part number 89018778. It looks like a resistor to me, but it was labeled as a module on the box. That is why I wasn't sure what term to use for it. I thought something like this would be plug and play and wouldn't need to be programmed.

bossier62guy · May 19, 2010

This is the part that I ordered in. It is part number 89018778. It looks like a resistor to me, but it was labeled as a module on the box. That is why I wasn't sure what term to use for it. I thought something like this would be plug and play and wouldn't need to be programmed.

That is a resistor/relay assembly and shouldn't require any reprogramming. This may apply to your situation:

http://208.109.104.11/forum/showthread.php?t=4700

How many wires are on the plug that connects to that assembly? Possibly 3, black, orange and purple?

gmtech4 · May 19, 2010

that resistor is definitely a plug and play item ,

now your fooked lol

you MAY need the overhead aux hvac control head (module)

did the tech try for a reprogram update or look for bulletins,check for codes ?

you'll have to scan it now or take it back ,i am curious to read the reciept with tech comments

bergersen · May 19, 2010

That is a resistor/relay assembly and shouldn't require any reprogramming. This may apply to your situation:
http://208.109.104.11/forum/showthread.php?t=4700

How many wires are on the plug that connects to that assembly? Possibly 3, black, orange and purple?

There are 3 wires. I think those colors are correct. I can verify tomorrow. They are labeled A, B and C. A is batt. B is control. C. is ground.

bergersen · May 19, 2010

The thing that is most confusing to me is if the problem is elsewhere in the system, why are these two resistors acting totally different?

bossier62guy · May 19, 2010

The thing that is most confusing to me is if the problem is elsewhere in the system, why are these two resistors acting totally different?

Hang in there....I'm still trying to find some more info on the circuit.

bossier62guy · May 20, 2010

That is a resistor/relay assembly and shouldn't require any reprogramming. This may apply to your situation:
http://208.109.104.11/forum/showthread.php?t=4700

How many wires are on the plug that connects to that assembly? Possibly 3, black, orange and purple?

There are 3 wires. I think those colors are correct. I can verify tomorrow. They are labeled A, B and C. A is batt. B is control. C. is gro

Managed to get my hands on the wiring diagrams and troubleshooting procedures that GM uses to diagnose your situation. The problem is most of the troubleshooting is done using a scan tool to command certain things to happen and your automatic HVAC system is a little more complicated than the standard HVAC system. What you purchased and installed isn't a resistor at all. It's called a blower motor control processor. The 3 inputs are ground, 12vdc (from the underhood electrical center) and a reference signal coming from the aux HVAC control module which is located about a foot away from the blower motor in the wheel well area. It is strange that your problem seemed to switch entirely after you replaced this part though. I'm going to keep reading a little more to see if there might be anyway to keep at it w/o throwing money away doing swap-tronics. Maybe Robert can offer up some ideas as well.