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Pete, GMC Technician
Category: GM
Satisfied Customers: 29096
Experience:  14 years GM dealership technician and training.
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2004 GMC: speed..low continue to blow

Resolved Question:

My 2004 GMC Sierra heater and AC fan will not blow, when pushing the fan speed button the light indicator goes up and down but fan speed stays low. You can feel heat or AC coming out but its a low speed. Also, have had it continue to blow after shutting off the truck. The heated seats work sometimes, and other times they shut off. Turn them on they work for awhile then go off. Maybe the BCM is defective?
Submitted: 6 years ago.
Category: GM
Expert:  Pete replied 6 years ago.
Hello,I will be glad to try and assist you with this,Welcome to Just Answer.


From what it sounds like here is that you have two separate failures.Both are very common.

First with the heated seats if this is just one side that is acting up like this this is usually caused by a faulty heated seat element under your seat covers.These tend to burn out and fail all the time and to correct this the covers have to be removed and the elements replaced.Usually it is the bottom seat cover element that burns out,this can happen to both seats around the same time or just one.

They may work intermittently if the connection that has burned out reconnects temporarily when seated and in other times they may shut right off.I believe this is what you will find at fault with this concern and not a BCM failure as this isn't as common.

A new element shouldn't cost more the $50 a side.

As for the fan not operating properly or staying on GM is aware of this problem and has a bulletin out on this concern.The correction is to replace the blower control module,this should be located under the dash near the blower motor.The control module is the component that controls the blower speed and shut off.What happens is it shorts out internally and causes the blower to be inop or stick at one speed and in some cases stay running with the key on.

The bulletin number for this is 06-01-39-002C

The part number you need for this new module is 89018964.

It shouldn't cost more then 1 hours labor to install this and usually less then $100 for the part.

These are the most common causes for these concerns here as I have had to replace quite a few of both to correct this problem.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!
Customer: replied 6 years ago.

For the heated seats, both sides act exactly the same. Somethimes the work for 15 seconds or several minutes, the seats don't even have to get warm before they shut off. Other times they work fine.

Expert:  Pete replied 6 years ago.
I just reviewed the diagnostics and the diagram for these seats and there is an additional bulletin on these for the heated seats being intermittent with this concern.

The fix is is to reprogram the seat control units under the seats.

The heated seat switch sends the signal to the seat control units(computers) under the seats.

Then the seat control units power up the heated seats.What happens is the control unit will either sometimes not power up the heater or will power it up and shut it down shortly afterwords and in some cases work like normal.

This updated programming has to be done by a GM dealer using their scan tool and GM computer in order to perform the programming.The charge for this is usually about an hours labor.

The bulletin number for this is 05-08-05-008.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!
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