2002 BMW 325xi. It has the GM 5L40-E auto trans.

The vehicle disengaged drive while moving. My g/f was driving the car and the transmission was engaged i.e. power was being transmitted from the output shaft of the engine to the input shaft of the trans and then from the trans to the transfer case and on to the drive shafts. Then suddenly there was no power being transferred to the drive shafts. When she stopped the car, placing in "P" ground a bit, which I assume is the parking pawl smashing into the parking gear because it was still turning. Once the shift selector was in the "P" position the car was not in park and the engine could still be revved. When choosing "R" with the gear selector, no engagement and engine could still be revved. Same for "D" and all of the low gears.

I have not gotten under the car to check out the drive shaft linkage or the transfer case yet. Assuming no major mechanical failure of the transfer case or drive shafts, what is the process flow when the gear selector is put into each position? I.E. what is the state of the Torque Converter Clutch when the car is in "P" and the ignition is not on, then what is the state of the TCC when the ignition is "ON" and the output shaft of the engine is rotating? What does the TCC solenoid do in each state? What does the Pulse Width Modulator Solenoid do in all states?

If its not a huge mechanical failure (there was no loud audible bang or clank when she was driving and the trans disengaged all gears. The problem is something like a false neutral if you've ever ridden a dirt bike / atv)

I just want a process flow diagram or some other informative representation of what happens when the gear selector is put to "P" position, "R" position, "D" position, etc.

1 Answer 1


It sounds to me that your transmission is going. The problem is that the gearing is probably loosing teeth and not engaging fully. I would recommend taking it into a shop to figure out the exact problem so you know for sure. If anything it could be doing more damage than you expect.

  • I think it would be making a lot of loud noise if that was the case as soon as I tried to engage any gear. I've got it lifted now and I'm gonna check out the transfer case and the transmission. Commented Dec 4, 2015 at 21:57

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