Information on the E46 Window Switches
Most people don't understand how the window switches work under the hood, so to speak. Below is the wiring diagram from the driver's switch block (S126) in a 4-dr which controls the driver's side front and driver's side rear windows. A1 is the GM5 or General Module (GM) which contains the relays which actually power the window motors. Notice there are four switches in the switch block, two for each window.
So what exactly is going on with the two switches for each window. You are probably aware that the switch has two settings for up and two for down. I will call them Half-Press and Full-Press. Half-Press will stop the window movement as soon as the switch is released and Full-Press will active the auto feature where the window will continue going up or down until it reaches the end of travel. A really convient feature.
When the switches are not touched they rest at position 0. Position 1 is a window open, half-press. Position 2 is window open, full-press. Position 3 is window close, half-press. Position 4 is window close, full-press. For each of the switches there is one signal wire going back to the GM. Signal SFFA is front driver window open. Signal SFFZ is front driver window close. Signal SFFHA is rear driver side window open and signal SFFHZ is rear driver side window close.
Ok, enough of the definitions. Now look at front driver window open, signal SFFA on connector X316 pin 1 very carefully. It is connected to switch positions 1, 2 and 4. Positions 1 and 2 make sense because they are Open positions, but, what's up with position 4, that's close, full-press. More on that later. Now look at front driver window close, signal SFFZ on connector X316 pin 4. It is connected to switch positions 3, 4 and 2. Positions 3 and 4 make sense because they are Close positions, but, what's up with position 2, that's open, full-press.
In both full-press positions both signals are connected and electrically there is no difference between them. So how does the GM know if you wanted auto close or auto open. That is determined by what switch position was detected just before. You had to go through a half press position before going full press! The problem with this scheme is if one of the wires is broken or one of the switches is bad. Imagine that signal SFFZ (close) didn't work and only SFFA (open) worked. In position 1, open half-press, there is no different since it doesn't need the SFFZ signal in this case. In position 2, open full-press, SFFA is still connected, but, it needs SFFZ to tell the GM that you want the auto feature, but, since we are imagining the case where it is broken the GM doesn't get that signal and the auto feature doesn't work! Most people may not even notice this because the next two positions are far more annoying. Ok, now position 3, close half-press. In this case signal SFFA is an open, but, SFFZ should have been connected, but, since we are imagining it broken, nothing happens. Now position 4, close full-press. In this case signals SFFA and SFFZ should both be connected as is the other full-press conditons, but, since SFFZ is not connected, because of our imaginary bad switch, only SFFA is connected and the GM interprets this as window close half-press. But, wait, we selected switch position 4 which is CLOSE full-press and the GM sees OPEN half-press. There is no way to close the window! If the bad signal was SFFA instead the case would be reversed and there would be no way to use the switches to open the window. In most cases the problem is the switch and not the wiring or the GM. It can easily be tested by removing the switch block and testing the various switch positions with an ohm meter. I hope this clears up how the window switches on the E46 work.
Window Switch Part Numbers
61316902183 2-door
Convertible Front Driver side (center switch for all up/down)
$40.09
at getbmwparts.com
61316902178 2-door Coupe Front Passenger side $40.09
at getbmwparts.com
61316902184 4-door Front Driver side (center button for rear window control
disable), old P/N 61318381518 $40.09
at getbmwparts.com
61316902179 4-door Front Passenger side window switch, old P/N 61318381514 $40.09
at getbmwparts.com
61316902174 4-door Rear window switch, old P/N 61318368921 $26.71
at getbmwparts.com
61316902175 Coupe Left Front window switch $47.73 at ECS Tuning
GM5 Repair Service web page.
BMW General Module III (GM3) Page