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  #1  
Old 09-14-2022, 12:36 PM
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Exclamation E53 3.0D Trans Fail Safe (GM Box) - Scratching my head (SOLVED)

Hi all,

This has been covered a million times I know... for the last few months I've been reading this forum and sure I've covered every single thread and still not found my issue! Anyway, here goes...

A few months back I was crusing along the motorway in 5th gear at a bit of a rate. Lets just say 70mph for the sake of argument although there may have been a bit of tax... The gearbox was happily in 5th and then out of nowhere I got 'Trans Failsafe Prog', the car violently shifted down to third and then thats where it stayed. Took it for diagnosis at my local BMW Specialist which just gave me a P0734 code which I understand to be incorrect ratio at 4th gear. Now when I drive I have 1st, 2nd and 3rd and once it tries changing to 4th I get the Trans Failsafe Prog.

Since then I have done a lot of research and have even tried to buy a replacement box (no luck there... they seem to be gold dust).

Last weekend I decided to make a serious attempt at fixing this and did a oil / filter change in the gearbox. There was a bit of a leak from the gasket, although this is now fixed. There were no alarming signs inside the oil pan, no chunks of metal and just the usual fine metal dust as one would expect with high mileage (155k miles). Mechatronic looked all good too so I'm pretty sure the box itself is fine.

Since then I've got myself a K+DCAN cable and scanned the codes myself using INPA. This has come up with:

Gangueberwachung 4 with notable figures such as 66c oil temp and 13.7 volts of power.

Now because the box appeared in good condition I was thinking that the valve body was probably the issue. Especially considering one of the original fault codes was "EGS Signal Line Disturbed" - A friend of mine looked at the wiring diagram for the mechatronic and seems to think that the solenoids are wired in series so if the 3-4th solenoid is dead then it won't change beyond there - this would make sense if the signal gets disturbed, dead solenoid means no signal...

However, today in INPA I have activated all 3 solenoids, they all make a noise and show 'Solenoid Valve #X is being correctly activated'. So this would suggest that the valve body is actually fine and the problem is elsewhere...

So before I rip the box out is there anything else I should be looking for as I'm not totally convinced the box is the issue, and I want to troubleshoot absolutely everything else before going to the expense of a used / rebuild box...

Apologies for the long post, I assure you all I have been reading here for a while, just never posted before now!

Thanks in advance!

Last edited by PixelBarnX5; 11-23-2022 at 08:39 AM.
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  #2  
Old 09-17-2022, 05:56 PM
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If youíve lost 4th & 5th gears then it could be the Ďtoilet rollí shaft thatís sheared (itís manufactured like the cardboard tube in the centre of a toilet roll). This means that the direct clutch hub is no longer driving the epicyclic carrier.









Phil
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Old 09-18-2022, 06:38 AM
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Hi Phil,

Thanks for your advice. I have done extensive research and this looks like it could be an issue. What Iím asking though is for anything else to check before dropping the box. I cannot find a replacement box anywhere and rebuilding is beyond budget.

The other thing is that there was no metal at all in the oil / filter / magnet. Youíd think that something like that breaking would result in at least some small chunks but there wasnít anything.
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Old 09-19-2022, 09:32 AM
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Although I agree that you might expect to see some metallic debris on the magnets from the direct clutch hub shaft failing, nevertheless this is a common failure in the 5L40-E and would produce exactly the symptoms that youíve described. The break can be very clean. Alternatively, it could be an issue (mechanical or hydraulic) with the direct clutch itself. Either way, I think youíll have to teardown the transmission to fix it.

If youíre handy with a set of spanners and money is tight, I would suggest that you do this yourself and buy a scrap box off eBay for the parts. Thereís several on eBay for around the £200 mark. Clearly, you need to check with the seller first that the scrap unit youíre buying didnít have the same issue (i.e. loss of 4th & 5th gears).

The transmissions are very straightforward to rebuild :
https://xoutpost.com/bmw-sav-forums/...-teardown.html
I can send you 5L40-E workshop manuals etc. if you want to do a bit of research first.

The next cheapest alternative is probably Birch Motors (£1194 incl. fitting).

Phil
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Old 09-19-2022, 04:03 PM
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Make absolutely sure your wiring harness connector at the transmission is totally clean and there is no debris or corrosion in the sockets. If you find any, clean it out, reconnect and check the transmission operation again. I had three separate incidents where water and dirt made its way into that connector resulting in a multitude of Trans Fail Safe errors and erratic operation.
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  #6  
Old 09-19-2022, 04:58 PM
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Quote:
Originally Posted by srmmmm View Post
Make absolutely sure your wiring harness connector at the transmission is totally clean and there is no debris or corrosion in the sockets. If you find any, clean it out, reconnect and check the transmission operation again. I had three separate incidents where water and dirt made its way into that connector resulting in a multitude of Trans Fail Safe errors and erratic operation.
Thanks for the advice. I will be checking this before dropping the box but because of the aforementioned fact that all the solenoids appear to be firing when I set them off in INPA, I expect the plug to be fine. Worth checking though.

Phil - thanks for the advice. By process of elimination I think you're probably right. It would make sense due to the way it failed in the first place. Birch Motors could be an option but owing to the fact they are 200 miles away from me that makes getting them the car quite complicated (and expensive).

I'm going to check the plug tomorrow and see where we're at. Might have a lead on a known good used box too, so there may be light at the end of the tunnel. If I can find a replacement box though I think I'm going to have a crack at rebuilding mine - I'm not too bad with the spanners...
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Old 11-23-2022, 08:31 AM
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Hi all,

Just thought I'd update you all on this one. In the end I replaced the box with a known good box, and gave the new one a full service, reset adaptations and all is good in the world.

I have since started to strip down the old box and I can confirm that RRPhil was correct and shaft that holds 4th and 5th had indeed broken. On first inspection it looked fine but it has actually started to come away and once fully removed we could see where it had actually gone. Pics to follow at a later date.

Just wanted to say thanks Phil, whilst it wasn't the "it's just this sensor" reply that I really wanted, it was a successful diagnosis. Furthermore I was told by an expert in such boxes that they have seen errors caused by the Gearbox ECU sending a random signal to put it into reverse, which is what can cause the snap. I don't know how common this is but they were saying they replace the ECU whenever they come across these sorts of failures.

For what it's worth I am planning to rebuild the old box over Xmas so will probably start a build up thread for it.

Thanks again guys!

Last edited by PixelBarnX5; 11-23-2022 at 10:53 AM.
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