Wow, thanks for your response. The passion for automotive engineering is commendable, even if it is a only a hobby!

Maybe this should be a new thread, but here goes anyway, what is the normal operational temperature of the transmission?

I seem to recall on my X that INPA reported that the transmission temperature was about the same as the coolant temperature. About 200F and something. Again, I thought this was high; I need to check INPA again.

In the meantime, I did point the fluke laser thermometer on the surface of the tranny fluid pan and it measured about 165F.

BTW I would be interested in looking at, or understanding the how of your PWM circuit or test jig. Up to you. I have a 1994 740il e32 that is down with transmission problems at the moment. Long story, this is what drove me into INPA/DIS world.

The PWM circuit could be used to modulate (for testing) the aux fan speed too!

j