What causes the blower motor resistor to fail on a 2000 Malibu?

Answer 1

Without actually performing a failure analysis on the specific resistor, there is no way to know what caused the blower motor resistor to fail. However, there are two likely causes, design and/or implementation. First a little info on the setup.

The blower motor is a brushed motor. One way to use the same motor and get different speeds is to vary the voltage to the motor. More voltage will give more speed, less voltage will give less speed. One way to "adjust" the voltage to the motor is to put a resistor in the power line to the motor. The resistor will "absorb" voltage and give off the absorbed voltage as heat. The Malibu uses 4 different resistors to create 5 total blower speeds. The 5th setting is with no resistor in line. As the resistor absorbs voltage and gives off heat, eventually the resistor will burn out and need to be replaced. There are many different quality levels of resistors. Some resistors are high quality and will last longer than the car will be used. Some resistors are low quality and will fail while the car is still in service.

Engineering selected the particular resistor used in the resistor pack. Perhaps, if the resistor burned out, the design is At Fault as the part wasn't selected correctly.

Implementation could be how the part was installed, perhaps the solder joint (how the resistor is connected) failed as the solder wasn't flowed correctly.

There is nothing you could have done as a consumer to increase or decrease the life of the resistor.