2007 GMC Envoy Denali, Blower Does Not Work On Any Speed

This 2007 GMC Envoy Denali came in with the complaint that the blower motor would not work. The customer stated that they had removed the blower motor and connected it to battery voltage and ground. The blower motor worked under this condition. This vehicle also has auto temperature controls as indicated by a digital display.

This diagnosis and repair applies to many GM manufactured mid sized SUV’s with automatic/digital HVAC controls.

2004, 2005, 2006 & 2007 Buick Rainier

2004, 2005  Chevrolet SSR

2002, 2003, 2004, 2005, 2006 2007, 2008 & 2009 Chevrolet Trailblazer

2002, 2003, 2004, 2005, 2006, 2007, 2008 & 2009 GMC Envoy

2003, 2004, 2005, 2006, 2007 & 2008 Isuzu Ascender

2002, 2003 & 2004 Oldsmobile Bravava

2005, 2006, 2007, 2008 & 2009 Saab 9-7x

I removed the two screws that held the hush panel in place. There are quite a few harnesses secured to this panel along with a module, four or five retaining clips holding harnesses in place, and a couple of nuts securing the module. They are all on the right side of the panel. It would be possible to leave those in place and work around them (not fun but doable) but it would be impossible to do this article with them in place. Getting the panel fully out of the way only adds a few minutes to the whole job and makes it much more accessible.


There are several ways to check this problem but my preferred way is to check the signal wires at the blower speed controller. I start by checking for power on the red wire and ground on the black wire. This was easily done by just back probing those two wires with the test leads from my multi meter. Both signals were present. The next step is to connect one lead to the black wire and the other to the small purple/white wire.


With the key off there should be a nominal 5 volt reading.


With the key on and the blower set to the highest speed setting the voltage should be a nominal 1 volt.

  • Highest speed             1.19 Volts (purple/white wire checked to black ground wire)
  •                                     2.57 Volts
  •                                     3.17 Volts
  •                                     3.66 Volts
  •                                     4.06 Volts
  •                                     4.48 Volts
  •                                     4.89 volts
  •  Off                              5.19 volts

Something of interest is that the less than 5 volt reading is achieved by the HVAC control head applying a pulse width modulated ground signal onto this wire. The 5 volt current is actually produced inside the blower speed controller. Initially one would think that if you just grounded the purple/white wire it would force the blower motor on. That is not the case however. The ground signal must be tapped on and off repeatedly in order to create a pulsed signal. I would not recommend doing such a test with the purple/white wire still connected to the HVAC control head circuit. Either cut the wire in a place where it is easy to splice back together or remove the terminal from the three wire harness connector body.


Since I knew the blower motor was good, power and ground to the blower speed controller were present  and the signals from the HVAC control head to the blower speed controller was good the diagnosis was a faulty blower speed controller. I had also checked the connector at the blower motor itself to make sure that connection was good and it was.

The next step is to replace the faulty blower speed controller. There is a slight problem with that because the original style with a three wire connector is no longer made by the OEM supplier. There are some aftermarket three wire units out there but I have encountered many people that have had multiple problems with those units so I do not recommend them at this time.

The new style blower speed controller is sold as a kit with the module, a new five wire harness assembly, splicing terminals,  a foam spacing washer and new screws. I personally prefer this supplier’s kit since the kit includes splicing terminals and heat shrink tubing. I do not like the splicing terminals with the translucent heat shrink tubing made onto the terminal. The internal terminals are not as good due to a non brazed seam and the heat shrink is too bulky and makes for a sloppy splice.

One other note: the OEM supplied blower speed controller is currently gray in color. There are some replacement out there that are black in color and as far as I can tell they are the first generation replacement controllers that GM and ACDelco rejected. There was an issue with those parts that may necessitate replacing the blower motor also. Especially if the original blower motor was manufactured by Bosch. The two technologies did not play well together. Of course if you have over 150,000 miles on your vehicle or if the blower motor had been making any kind of strange noises before it failed, you may want to go ahead and replace the blower motor anyhow.

Note that I cut the wires in a staggered pattern. This does a couple of things. First it makes for a cleaner spliced harness as it reduces the overall bulk of the harness. Second by cutting and splicing one wire at a time the repair can be done without disconnecting the battery or removing the blower fuse. Of course if you do not feel comfortable leaving power on the red wire please remove the blower fuse from the under hood fuse block. I do not recommend disconnecting the battery at all. The reason being is that a system recalibration is always initialized anytime the battery power is disconnected and reconnected from the HVAC control head. Many times the recalibration process will find a failing mode door actuator and the result is airflow will only come out of the defrost vents. Not something you want to deal with in the middle of a hot summer. If you do plan on disconnecting the battery go ahead and buy a new actuator ahead of time.


If you will pay close attention you should notice that the plug position is towards the firewall side of the module where the original is toward the seat side of the module. This is the way it supposed to be.


The wires wrapped up in a neat harness and everything properly installed. By the way I do not know what the reddish orange goop is dripping down from the top of the dash. I would assume it was some sort of melted candy. i did not want to touch it and have it smear all over the place.


As mentioned earlier there is a foam spacing washer included in the kit. It has a self adhesive side and should be installed in the position shown below.


Another one fixed.

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