Power Window Problem

[123NotIt]

About a month ago, my passenger side power window started getting really stubborn. I would have to press the switch quickly a few times in order for it to respond. But now the window has stopped working completely.

Here's what I did to troubleshoot:

First I removed the front door panel, then removed the front power window motor. I tested the connector with a multi-meter and when I hit the switch, the meter read +12.2v or -12.2v. This told me the motor was in fact getting voltage and I could rule out the switch or the circuit being bad. The next step was to test the motor itself to see why it wasn't spinning even though it was getting voltage.

To test the motor, I removed the rear passenger door panel and the rear power window motor and swapped it for the motor from the front window. It worked! - But why did the front power window motor work fine when I hooked it up in the rear door but it didn't work in the front door, and at both places the multimeter read the necessary 12v?

Please help me. Any ideas would be greatly appreciated.

[BMWLotAttendant]

Sounds like you need a new window regulator.

[123NotIt]

The window regulator seems to be okay because I can move the window up and down with the motor detached. used The problem is - with the motor detached from the regulator completely and just hooked up to power, so there is not mechanical restriction - it won't spin. But if I hook it up in the back it will spin. When I test the electrical leads with a multimeter, both the front and the back are getting 12v power. Why would the motor spin on one but not the other when they are both getting the same power. ghead

[94 325is]

i dont know how many prongs the plug has but you can see if the rear plug is getting power to same prongs as the front. it could also be a ground problem if it grounded through the plug.

not many ideas other than that .. used

[123NotIt]

The plug has 2 prongs. To test the ground problem I used the ohm meter to test the resistance between the prongs and the car's frame. I noticed something strange though when I had the positive prong hooked up and I pressed the switch. The resistance on the ohm meter went to infinity. This only happened in the front, not the back. I remember from physics class that V(voltage) = I(current) x R(resistance). So, if the voltage was increasing when I hit the switch and the resistance went to infinity, this meant that there was little or no current. When I thought about this more, I realized that maybe I should check out the switches more (maybe they are dirty or something and so not passing any current). Sure enough, it was the switches! I was thrown off before when I tested the switches and I saw the correct voltage change, I needed to see that they weren't passing any current to see the problem.

It all works now!!! Thanks to Blondestar - 'ohh...you wouldn't believe it...the switch is actually bad'

Thanks for the help though BMWLotAttendant and 94 325is!