Blower Motor Issues

khobbs1khobbs1 Member Posts: 1
edited May 2015 in Toyota
Hey guys. I come here after googling first and trying some troubleshooting based on various things I found for my 2010 Toyota Highlander blower motor.

The issue is that my blower motor operates intermittently. Here are the symptoms and what I've done so far:

-Sometimes it works and sometimes it doesn't. It seems to be dependent on weather (in the sun for awhile and doesn't seem to like that), although lately it doesn't really seem to matter. Had it in my garage yesterday and it just works some times and not other.
-If it works, all speeds work (full range). That makes me think it doesn't have to do with the resistors, although I can't find the electrical schematics for the car.
-All fuses are fine
-I have jiggled all wires and can never get it to work (if not working at the time) or to not work (if working at the time), so I don't think loose wires are the issue.
-I put a multimeter across the leads going to the motor and always get voltage. When the car is on, it's about 13-14V, and when it's not running just above 12V.
-The rear blower motor works perfectly, 100% of the time
-Light physical agitation of the motor doesn't make it come on or go off

My main question is what is the 3rd lead going to the motor? The two bigger leads are the voltage, but that seems to always be there, even with the car off. I'm guessing the 3rd lead is some control signal for the motor but not sure. I can't ever get a voltage on that lead, but I'm not sure I'm even supposed to. When the motor was supposed to be on and it was working, I unplugged it and checked the voltages, but got the same readings as when it wasn't working.

It seems to me that the power source is okay, but maybe it's something with the control circuitry that's loose or has a poor ground somewhere? Thanks for the help, guys.


  • turbo64turbo64 Member Posts: 10
    The contacts inside the switch get worn out. The lower speeds naturally because one we get cool what do we do, turn it down that's right.
  • thecardoc3thecardoc3 Member Posts: 5,696
    Pin 23 red wire is the blower control output from the AC amplifier. Diagnostics on this system require the use of a scan tool that supports the electronic AC control system with reporting data stream, bi-directional commands and codes. While the AC amplifier is on the high speed CAN data bus, the control head communicates with the amplifier on a dedicated LIN bus wire and does not communicate directly to the scan tool.

    The command from the amplifier to the blower motor is duty-cycled. The square wave when viewed on an oscilloscope would have a lower limit of around .8v and an upper limit of 4.8v. While a voltmeter can be used what you would see is a voltage that would vary from around 1.2v at low speed to 4.5v at high speed. Since this is a command output from the amplifier just to the driver (transistor) that controls the blower speed it is a high impedance signal. That means if you are trying to check this with a test light (low impedance) it would look like no-power. A test lights needs to flow a lot more current than what the blower control circuit would put out.

    Some others test that you could do would be to try measuring the duty cycle of the command which would be low (less than 15%) when the blower is at high speed, and high (more than 85%) when the blower is set to low speed.

    Beyond proving that the signal to operate the blower is in fact reaching it, and having proven the powers and grounds, which would mean you have a bad motor assembly you really need full function scan tool to do anything else. The odds are you can't even just replace the control head or amplifier if you actually did manage to prove that one of them has failed. You'd still likely need a scan tool that can do flash programming as well as any system initializations.
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