Another trans fail safe
 

I think I tried my best searching here but still didn't find luck.

So the 4.8is tranny has just been recently overhauled by an indy. Shifts buttery smooth I can tell you. Following day after driving 3-4 km, car wont start and the trans fail prog error appears on the dash with the trifecta lights on as well.
Checking with INPA, the trans control unit could not be accessed and at one point the engine ECU as well. When the engine ECU could be accessed, fault code says something about CAN bus signal not returned or something.

Leaving the car off for about 2 hours the car will start again and could be driven with the sports or manual mode intermittently inoperable.

Sounds like a communication issue to me but not really sure where to look at. I also dont have access to the wiring diagrams at the moment.

Would really appreciate your guidance.

Thanks
Joy
E53 4.8is 2005 at 223000km




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Tried checking with INPA again while the engine is running but still there is no response from the gearbox control unit it says. Car can be driven but no sports or manual mode option. 🤕🤕


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Found this
Intermittent No Start, Transmission Failsafe Mode, Engine Shut-off - Bimmerfest - BMW Forums

I'll update later about progress........

Sounds like a dead battery.

I forgot to mention that - battery is brand new!

What's the voltage on the battery when connected to the car?

What's the voltage on the battery when the car is running?

12.3 ignition on
13.8 engine running
Battery is brand new - Bosch S5


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I would look at the cable that is attached to the TCM. Could be corrosion in the connector terminals.

Well the X would always start now. Error message is gone for now.
upallnight is right, it was just the connector to the TCM.

Now, on to the next problem!! Looks like a front diff change is coming!!!

That didn't last long! TCM is not responding again.

Is the TCM connector supposed to be dry? I notice the contacts always have oil in it when I pull the connector out.


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