Rick's Free Auto Repair Advice

Test a Honda Blower Motor

Learn how to diagnose and test a Honda blower motor

If your Honda blower motor isn’t working, chances are you have a bad power transistor. Honda uses a power transistor instead of a traditional blower motor resistor to vary blower motor speeds. This article explains how the system works and how to test a Honda blower motor.

How a Honda controls the speed for its blower motors

The blower motor circuitry in a Honda is different than the traditional switch/resistor setup found in other vehicles. Power flows to a blower motor relay first. When you turn the key on, the relay provides power directly to the blower motor. Switching the fan on tells the heater control unit to send a pulsed voltage signal to the power transistor. By pulsing the transistor at different rates, the control unit can alter the speed of the blower motor. At high speed, the transistor provides ground almost full time, but switches the blower motor ground connection on and off several times per second to lower fan speed. This setup completely eliminates the need for a resistor and all the wasted energy the resistor consumes.

blower motor wiring diagram

Test a Honda blower motor

To test a Honda blower motor, simply disconnect the power transistor from the blower motor and provide a jumper to ground the blower motor. Turn the key to the RUN position and turn on the blower motor. The jumper ground should cause the motor to run at high speed.

To get a really good idea of whether the problem is the control unit or the power transistor, you need a scope. However, most techs don’t both testing the transistor because it’s the most common cause of blower motor failures.

Disconnect the electrical connector to the power transistor. Then connect the ground clip of the test light to battery +voltage and quickly touch the probe to the terminal on the power transistor where the blue/yellow wire used to attach. If the blower motor starts, the power transistor is OK. If not, replace the transistor.

FYI, shops report that the power transistor is usually the cause of the problem when a blower motor fails to run. The part is only available from Honda (that I know of) and costs about $25.

If the power transistor is dead, it may also cause the AC to not operate. So if you have both problems, fix the blower motor problem first before moving on to the AC issue.

© 2012 Rick Muscoplat

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Posted on by Rick Muscoplat



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