I read for about 2 hours last night of the search results of all the “good” stuffs about the 722.6 transmissions. While I got educated on the topic, I did not find an exact situation/cause/solution as I experienced yesterday afternoon.

The car is a 1997 E320 with 75,000 miles. Earlier on its life, the transmission ECU (Electronic Control Unit?) was replaced. The fluid is original.

Occasionally I experience a slight vibration when the car downshifts from 2 to 1 (coming to a stop in W setting but happens in S as well). It does not happen often (once a week) and I can live with that.

Yesterday afternoon while driving, the car stuck in 3rd gear and it won’t upshift. I got home and shut it down, and started reading the search results of this particular transmission. There was NO Check Engine light.

This morning, I drove it to work and it shifted perfectly. It went smoothly through all the gears (2->3->4->5) and in 5th gear; the rpm was 2000 at 55 MPH.

So I am a little stumped here. Is this an early sign of trouble for the transmission? What can I do to correct the potential problems? Although there are many potential causes here, is the data plug the most probable cause here?

The car does not have any transmission fluid leak. I am sure a filter/fluid change might help but my gut feeling is that it is not the cause of the problem.

Any advice, insight, and experience is appreciated.