2004 745Li Transmission Failsafe

Hello everyone. I'll start off by saying thanks in advance to anyone who can shed some light on my issues. I've found this forum to be a great source of information when it comes to these beautiful cars.
My car is a 2004 745Li with a transmission issue. I've had it for about a year now and it's always shifted a little rough. Worse when cold. When driving down the highway and in 6th gear it will randomly slip out of gear and rev up about 1000-1500 rpms for about 2 seconds and go back into gear. On occasion it will be bad enough to bring up transmission Failsafe on the dash and then it won't even go into 6th gear. Lately when starting the car, I'll put it in gear and it will automatically say transmission Failsafe and refuses to go into drive or reverse. Please help. Awhile back I had changed the integrated supply module in hopes that it was part of the issue, but no luck there.

I would also like to add that less than a year ago I did replace the battery and alternator.

Hi,

Quite a common problem, the transmission has detected a fault and shifted to 'Park' to prevent damage to itself. It is likely a low oil pressure issue caused by low fluid level or a cracked bridge seal between the mechatronics valve body and the oil pump inside the main body of the transmission.

If you can get hold of INPA read the error codes from the EGS module and post them up, I would suspect you have 'Gear check errors' where the transmission is slipping.

I had this issue, sometimes I could put the car into 'R' and hit the gas and it would go forwards! Issue was the low oil pressure not being able to apply enough pressure to the clutch packs.

The bridge seal design has been revised by ZF to make it more robust.

Stuart

Thanks Stuart. I'm going to look into that. Was this something that you were able to fix yourself? I'm a very good mechanic, but the bmw transmission isn't my specialty. I appreciate any response.

No problem!

It's not that difficult, just take your time, if you have some ramps like at a workshop or something then it's really easy!

My trans finally blew on the way home, luckily I managed to limp it back to my girlfriends house! As soon as I took it out of drive it would stay permanently in park even when cooled down, these cars are seriously heavy to be pushing around!

I ended up pulling the pan and mechatronics in the parking space.

Here are some pics:



Pan and mechatronics removed



Mechatronics in the kitchen!



This was the cause of all the problems, this is almost certainly what's wrong with yours.



This is the valve body with the electronics module removed, notice the grey film? This is debris from the clutch packs, it's conductive and can cause issues with the speed sensors. It's worth cleaning as much of this off as possible.



Makeshift shelter! It was raining!



New seal fitted



My mate helping me refit it!

The seal itself costs around £5! A cheap fix to an otherwise very expensive transmission problem!

I have heard this and the connector sleeve an leaking oil pan are the three most common problems, a local ZF specialist has confirmed these boxes come back for repair and these are the issues they all have, very rarely does anything mechanical go wrong with them. The mechatronics is pretty intelligent and will go into failsafe immediately if something is wrong to avoid causing internal damage. It may be a nuisance but at least it's not wrecking itself!

Hope this helps, any questions just ask.

Stuart

Wow. Thanks Stuart! I couldn't have asked for a better or more detailed response. I'll get going on this immediately. I'll let you know what I come up with.

Where can I go to get the bridge seal Stuart?

Hey Stuart, just wanted to update you and say thanks for all of your help. Turned out that I had an oil pressure issue. The previous owner of my car did some not so professional repair work to a leaking transmission line. Long story short, I fixed it myself and I'm doing good so far. Thanks again.

I've had it for about a year now and it's always shifted a little rough.