My 2005 GMC Canyons blower motor works only when the switch is placed on the highest position. Is it the switch, or the blower motor, or is there something that I am not thinking of?

{: ) Check out the J-case fuse (square) labeled BLWR 40amps at the underhood fuseblock. This fuse is the source of power to the blower motor when position 5(max speed) is selected. If this fuse is tested to be okay, you need to access for the blower resistor connectors. Turn ignition on, and set blower to max speed (#5). Probe on the blower resistor terminal (orange wire) and you should get 12volts, also probe the terminal (red wire) which came from the 40amp fuse. 12v should be present on these two terminals at the blower resistor when at max blower speed. Particularly on the orange wire, if you don't get 12volts when at #5 position, it 's probable that the blower speed control switch is faulty. But if you did got 12volts during the procedure, then you should replace the blower motor resistor. Goodluck.

you need to replace the blower motor and the blower motor resistor to correct you problem

The resistor is most likely bad but should still work on the highest setting.Would check pigtails to the resistor and to the blower motor for burnt or discolored wiring.You can try tapping the blower motor and wiggling the wiring harness too see if it will work on the highest setting. It is possible that the blower motor is bad as well typically when you lose the speed selection it is the resistor but you should always have high speed.

First check and see if you have voltage at blower motor with key and switch on, with test light, if you do have voltage, blower motor bad, replace it, if you don't have voltage at blower motor, next to it, is where the blower motor resistor is at, follow the wire from the blower motor to it, check voltage there, should have voltage, if you do replace blower motor resistor, resistor cost about $45.00 at auto parts.If I can be of more help. please let me know.

The switch or the wire harness at the blower motor has gone bad. The highest setting 5 has no resistor, so the blower runs on high but the high current flow ends up burning up the switch's contact on that setting or the resistor wire harness at the blower motor has gone bad. Common would be the switch it self, if the switch is good. Then it's going to be the wire leads at the speed resistor by the blower motor under the glove box by the passenger leg compartment. Keep me posted, be glad to help you get your Sierra running 100% again soon.

Replace the blower motor resister,it is mounted right next to the blower motor,it has a lug with about 7 wires on it.Just unplug it and remove two screws to remove the resister.This controls the speeds for the blower motor.The blower motor is the cause of the resister failure.Even if the motor seems to sound,and run fine,it is pulling to many amps.

this problem is caused by a defective blower speed control resistor, it is located near the blower motor, very cheap to replace, part is around $35

Blower motor resistor. Located next to/ near the blower motor itself. These are common failures for no high speed blower operation.

if there is swich problem
if there is wire problem
if there is loos wire
if all ok check power suplly

The Canyon has an inherint problem with the Fan Power cable being loose. When I say loose...I'm saying that you need to adjust the wires and then take a zip strip to tighten it up.

Passenger side under the dask are 2 cable hook ups. the one on the farthest right (Only 2 wires going to the plug) is the fan power cable. Jiggle it while the fan is on position number3 so you can hear when it comes on!!!