Help me with the terminology please... what's pwm?
Pulse Width Modulation
In this case, like Macrobb said, the E4OD/Early 4r100 just use an on/off solenoid. Think light switch, light off - no lockup, light on - lockup, but that light only has a pinhole to shine through. The light is on, but only a little light "leaks" through. If you looked at the controller output on an oscilloscope, it would be a square wave, but if it was disengaged, it would be off, engaged it would be on.... something like this:
___________________--------------------____________________--------------------
That it, all or nothing, a constant signal.....
PWM, the solenoid is controlled by a variable signal. Same light, but flip the switch really fast.... this time, the bulb has a larger hole for the light to go through, but the amount of light getting through is less, because the light isn't on 100% of the time.
So it would be controlled by a signal that looks like this:
____________----__________------_______--------______-----------_______---------------
Until it would eventually stay 100% to stay fully locked.
Or another way to look at it, non-PWM would be they way a lot of small engines are used, idle, or full throttle.... one or the other, PWM is like riding a skateboard... you start off slow, but the faster you go, your kicks get faster until you are going as fast as you can.....
This is how a lot of variable speed things are controlled now. For example, the electric cooling fans in newer vehicles...... they are not fed 12 volts through an on/off switch. They are fed 12 volts through a controller, that will quickly switch the 12 volts on and off to just "bump" the motor to maintain the speed. In the skateboard analogy, kicking just enough to maintain the constant speed you want to go.