Transmission fluid issue !?

[Mark3377]

Hey everyone. I'll try to keep a long story short but still give the main details to make sense.

My BMW is a 2000 740iL and I have it since 2005.
In 2011 I changed as much of the trans fluid as I could with Mobil 1 ATF and added a new FILTRAN filter. Did the proper top-off procedure at operating temperature.

Fast forward to 2018 and this issue started and it's still going on but only once in a while - the transmission gets stuck in 2nd or even 1st gear and just revs up but doesn't change gears up. At times, it fixes itself as I drive a few blocks or I pull over if I can and shut off the engine for a minute. When I go again, it may be ok or still getting stuck for a while but eventually gets going well. No trans fail message ever. Sometimes I go weeks without any symptoms and then they come back one day or a few days. Can't really connect the symptoms to any particular details (hot or cold weather, rain, long or short drives) but maybe it seems that it has more chances to happen at low speed/traffic.

I've done all the reading I could about the issue and it can be due to a lot of reasons:
-wire harness inside trans pan
-other sensors or parts I don't remember the name for
-wires under the car that may have been hit/exposed from road debris causing a short circuit especially when wet
-etc.

I noticed over the years leaks under the engine and it seems to be ATF but it was coming from the power steering container so once in a while I just added more fluid. I could never tell if there was a also a leak from the transmission or just ATF from power steering.

I figured if the trans was leaking, I would be low on fluid so yesterday it dawned on me what turned out to be a stupid idea. I had the right/passenger side lifted 5 inches to check wires, etc and it dawned on me that if the car is up on one side, maybe I could add some trans fluid given that the angle of the car was lowering the fluid level compared to the fill plug (turns out not).

I slowly opened the fill plug but eventually fluid started coming out and I lost a puddle of about 1 square foot of fluid on the floor before I managed to fit the plug back in.

Took the car today to a shop to have the fluid topped-off properly with the car up in the air (much easier than crawling under car on my garage floor).

So I make sure they do it right... engine running, car up in the air, open fill plug at operating temperature. But guess what... fluid starts coming out. The guy puts the plug in right away. I was thinking this can't be. I figured maybe just some little fluid came out and then it'll stop so we tried again. Plug out, fluid comes out, plug back in.

I was super confused. Based on these things, it looks like the fluid level is ok. But how about the fluid lost already yesterday and now at the shop? Was that extra fluid I managed somehow to add back in 2011? How could I even do that? The trans pan was operating temp back then.

Anyway, we decided to leave it as is because based on these events at the shop, the fluid level is ok. I'm still confused.

Any ideas are welcome. Thank you.
Mark

[acspecialists]

If you are sure the car is level and the temp is correct with the car running let the fluid out. Unless you were there watch the last time there could be extra.

As for your problem I have had several with my car. Check out Timm's fix for the shifter contacts, I've done it and it works. Next would be to have a look at the plugs on the TCM. My trans was acting up and using INPA I could see no output shaft speed. After replacing the sensor and trans fluid I ended up just cleaning the plugs and pins on the TCM to fix the problem. I drive my car at the track and have yet to have a mechanical problem with my transmission.

[Mark3377]

Thanks for your answer. If you have a link to Timm's fix, that will be great.
I'm busy getting ready to move out of state and will do more research/work when I'll have time. For now, I managed to get a trans dipstick and I installed it a week or so ago. I know that it won't fix the issues I described in my original post but it sure is satisfying to be able to add ATF through the dipstick whenever I'll do a partial flush or just to top it off if needed.

[Timm]

The quickest way to check this is with diagnostics such as INPA - you need to check the reported Transmission Temperature. The system is designed to hold the lowest gears if the transmission temperature is excessive. Sometimes the gearbox temperature IS excessive due the the failure of the heat exchanger - sometimes it is the harness or temperature sensor itself.