Fiero Power Window Controller

This is a description of an automatic "one-touch" power window controller that I have designed specifically for the Fiero. I just felt that this feature found on many modern automobiles was desperately needed for the Fiero. I wanted a device that kept the manual functionality, but if the button is tapped for less than 0,5 seconds the window will go up/down to the limit and shut off automatically.

Design goals

image of power window controller When I designed the system, I had several design goals in mind:

- Factory design

- Simplicity

- Intuitive operation

- Safety

- Ease of installation

- Diagnostics

Factory design

The unit should have the "look and feel" of modern car electronics. I should behave like it always belonged there. I wanted a unit that might have come from GM, if it had been available at the time.


I tried to keep the unit as simple (and hence as cheap) as possible, while still maintaining my design goals. Except for the power switch semiconductor, I only used standard parts. Unfortunately many small parts still do add up, so the total does not compete with a Korean pocket calculator, but considering the price of most aftermarket add-ons I think it's worthwhile. Click here to read the circuit description


The operation goes like this:

Safety feature

Automatically closing a window can be dangerous, especially if the shut-off threshold must be set high (as on the Fiero to wedge the window glass into the door seal tightly). Someone may catch their arm in the window, and not be able to reach for the switch to stop the system. This is especially true for children. To prevent any accidents, the system has a safety jumper, that disables the auto-up function if set. In this mode, the window only goes down automatically, but the button must be held down while the window goes up, just the way it is now. With or without the safety jumper, if the ignition switch is off, the system is disabled, again just the way it is now. If you leave your kid in the car, you should remove the keys anyway.


I wanted installation to be as painless as possible. There are only three wires to cut and splice, and going back to stock only takes a few minutes. Click here to read the installation instructions.


The unit continually performs selftests to diagnose problems automatically. I put a lot of effort into the diagnostic features. Since the CPU can determine many fault conditions, I chose to include a diagnostic LED that can display trouble codes, much like the ECM's check engine light. If the CPU detects a fault, the LED comes on. If a diagnostic jumper is set on the controller, the LED blinks a trouble code that can be used to diagnose the problem. BTW, the controller does not need an extra fuse, it is protected by the power window circuit breaker, because the PROFET will shut off much more precisely than a circuit breaker ever could. So, no extra protection is necessary. The controller itself only draws 12.5mA when not in use, BTW. This increases to approx. 110mA with the relay on, not counting the power window motor of course. If the ignition is off, the unit is not powered either.

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