2003 Chevrolet Silverado, Blower

I have been asked many times about the auto blower control on 2003- 2007 Chevrolet Silverado Classic and GMC Sierra Classic trucks so I decided to take some readings on my truck. This also applies to the Tahoe, Yukon, Avalanche, Escalade and Suburbans of the same era with auto a/c controls. The blower control processor is located under the passenger side of the dash.

There are a couple of 7 mm headed screws that have to be removed in order to drop the hush panel down far enough for testing. There is a third screw that is over the transmission hump that has to be removed if the panel needs to come all of the way out.

After dropping the panel down enough to test, I checked for power on the red wire, ground on the black wire and variable voltage on the purple/white wire. Of course I had all of the proper readings. My blower works fine. I was just testing for informations sake.

I did notice something that seems a little strange. With the key off there is 5.2 volts on the purple/white wire.

With the key on and the blower set to low the voltage was 4.91 volts.

As I adjusted the fan speed to high the voltage was pulled down to 1.632 volts.

My conclusion is that the signal wire from the control head (purple/white) goes to an open circuit when the key is off and the blower control processor is actually feeding out a nominal.

5+ volt signal that it needs to have pulled down by applying a ground from the control head assembly.

The two most common failure symptoms with this part are an inoperative blower motor or a blower motor that will not turn off even with the key off. For testing information please see these repair articles. 2004 Chevrolet Silverado Blower Will Not Turn Off. and 2005 Chevrolet Tahoe Blower Not Working  (video).

This part has been updated several times and here are links to a detailed repair article and parts information.