General Motors Informative - Fixing Power Steering Failure
I own a 2005 Saturn ION and commute about 20 miles daily. About a year and half ago my power steering dc motor was shutting off by some internal process. Since I am an engineer I found this problem interesting. I tried to understand what would cause the power assist to shut off. I peruse I few web forums and found their explanations for the failure, didn’t match what I was experiencing. The two main WEB reasons are bad fuses and bad motor. A fuse, such as the ones in the ION is a piece of wire connecting between two terminals. When the current flowing through the wire exceed the rating of the fuse it burn out, like a light bulb. It does not come back. If you can power cycle (turn off then back on) your ION and it clear pwr str then it is not a fuse. Unless the fuse holder is loose and that kind of mechanical failure would be notice on the dealership lot. Base on my understanding of DC motor which is ok. A DC motor with a short would blow the fuse and disable the power steering until fuse was replaced. Then it would blow again as soon as the car turns on. If the DC motor coils had an open path then motor wouldn’t work. Thermal expansion of materials could cause a physical break to expand. That would disable the motor until it cool off. Again If you can power cycle (turn off then back on) your ION and it clears pwr str then it isn’t thermal expansion.
I believe the real cause of the power steering failure is a bad thermal sensor, or a thermal sensor circuit with too high of a gain. An internal microcontroller decision point set too low could cause the failure. Why a bad thermal sensor? I drove all winter and my power steering was fine. Once the temperature went above 75 degrees the power steering started to fail again. The sensor reports a higher ambient temperature in the summer. The since it a DC motor sense circuit the micro shuts down the power steering. At lease that is what I belief my car is doing.
It should be possible to use a heat gun to simulate this failure, if you know where the sensors are located.