W163 ML270 2002 722.6 won't engage any gears!

[Arudge]

The main problem I have is that there's an awful lot going on but very little is actually reported by the software.

I have also coasted to a halt and reduced to tickover, but has no codes. And 10 mins later it was fine.


Mmmm, i believe they call it character building!

 

[Blueyes1971]

Yeh that's exactly how I'm putting it together in my mind....and it makes sense...so we will see when the switch arrives...I suspect tomorrow...if that still doesn't sort it , then it could still be a fault with the selector module itself...but it has never seen spillage...so it would be a long shot...but the more I think about it the more the brake switch made sense...which is why it was the very first thing I did was ordering it...it just makes sense....but I've been confident before about issues....everything else I'm doing or looking at is really just to cover all the bases I can while awaiting the switch.
Should know tomorrow hopefully ...i will post as soon as it arrives and I've installed.
Thanks again

 

[Steve@Avantgarde]

This isn't an electronic issue here..but a mechanical failure inside the gearbox, possibly a split clutch pack, drum or TC failure.

I will state why.

The gearbox ECU controls only the shift element to the gears only and signals from the ABS system. It needs a comms line to the engine ECU for pattern shift vs engine speed. The gearbox ECU is clearly in an operable state, its seeing the fault codes from the gearbox, its not flagging any comms issues with the engine ECU, if it did see anything it would list and then default to gearbox limp mode, which is 2nd gear.

Even if you disconnect the gearbox ECU totally from the car, start the engine you can still pull it into gear, it will thump straight into 2nd, or reverse, and the car will move. Electronics on this age of car will not override mechanical elements.

The 2 fault codes that indicate your failure are the last 2 on the list "the gearbox has an impermissible ratio" in other words the drum speed of the transmission is not matching the output speed or possibly the TC speed is not matching the drum speed. Either way it indicates a total loss of hydraulic pressure, meaning a loss of drive.

You say that you have experienced slipping or falling out of gear previous to the loss of drive, that is the biggest clue here yet that something was on its way out and now it has let go totally.

You also say you have checked the TC to see if it is spinning...well you will see it spin, its bolted to the flywheel, even if the internals have failed, it will still spin at 700rpm at idle.

I would be draining the oil and dropping the sump rather than taking the selector apart and looking at the electronics.

 

[Blueyes1971]

Thanks for you input Steve.
So you said you would be draining the oil and dropping the sump....
But you didn't say why....what you looking for ...checking etc other than particulate in the pan?
Thanks again

 

[Steve@Avantgarde]

Check the condition of the oil, opening the filter to check for debris and seeing if there are any bits of gearbox in the sump that should be attached to gears!

 

[Arudge]

This isn't an electronic issue here..but a mechanical failure inside the gearbox, possibly a split clutch pack, drum or TC failure.

I will state why.

The gearbox ECU controls only the shift element to the gears only and signals from the ABS system. It needs a comms line to the engine ECU for pattern shift vs engine speed. The gearbox ECU is clearly in an operable state, its seeing the fault codes from the gearbox, its not flagging any comms issues with the engine ECU, if it did see anything it would list and then default to gearbox limp mode, which is 2nd gear.

Even if you disconnect the gearbox ECU totally from the car, start the engine you can still pull it into gear, it will thump straight into 2nd, or reverse, and the car will move. Electronics on this age of car will not override mechanical elements.

The 2 fault codes that indicate your failure are the last 2 on the list "the gearbox has an impermissible ratio" in other words the drum speed of the transmission is not matching the output speed or possibly the TC speed is not matching the drum speed. Either way it indicates a total loss of hydraulic pressure, meaning a loss of drive.

You say that you have experienced slipping or falling out of gear previous to the loss of drive, that is the biggest clue here yet that something was on its way out and now it has let go totally.

You also say you have checked the TC to see if it is spinning...well you will see it spin, its bolted to the flywheel, even if the internals have failed, it will still spin at 700rpm at idle.

I would be draining the oil and dropping the sump rather than taking the selector apart and looking at the electronics.

This isn't an electronic issue here..but a mechanical failure inside the gearbox, possibly a split clutch pack, drum or TC failure.

I will state why.

The gearbox ECU controls only the shift element to the gears only and signals from the ABS system. It needs a comms line to the engine ECU for pattern shift vs engine speed. The gearbox ECU is clearly in an operable state, its seeing the fault codes from the gearbox, its not flagging any comms issues with the engine ECU, if it did see anything it would list and then default to gearbox limp mode, which is 2nd gear.

Even if you disconnect the gearbox ECU totally from the car, start the engine you can still pull it into gear, it will thump straight into 2nd, or reverse, and the car will move. Electronics on this age of car will not override mechanical elements.

The 2 fault codes that indicate your failure are the last 2 on the list "the gearbox has an impermissible ratio" in other words the drum speed of the transmission is not matching the output speed or possibly the TC speed is not matching the drum speed. Either way it indicates a total loss of hydraulic pressure, meaning a loss of drive.

You say that you have experienced slipping or falling out of gear previous to the loss of drive, that is the biggest clue here yet that something was on its way out and now it has let go totally.

You also say you have checked the TC to see if it is spinning...well you will see it spin, its bolted to the flywheel, even if the internals have failed, it will still spin at 700rpm at idle.

I would be draining the oil and dropping the sump rather than taking the selector apart and looking at the electronics.

Just to broaden my own understanding.....i have also experienced this complete loss of gears and complete loss of accelerator function without any obvious reason. On the last occurance I was powering around a slow bend, eased off the power and possibly touched the brakes. 're applied the power and there's nothing there, and I mean nothing. Engine has dropped to turnover and we coast to a stop. No response to the accelerator, may climb to 1000rpm, no codes on a generic code reader. Turn ignition off, leave it 10, turn back on and everything is fine.
I haven't found the root cause yet, but I'm working on it.

 

[Blueyes1971]

Your experience suggests that as old as 2000 models...( your CLK) the trans can completely disengage giving you exactly the same symptoms as mine...restricted revs in drive or reverse but no movement..
And mine is two years younger....go figure.
Brake switch arrived this morning , fitted it and no change to the issue at hand...although I know it required replacing so at least another job done....hoping the cooler arrives today so I can install that along with a new coolant radiator...test for flow from the pump ( I'm guessing they should be a specific flow rate also)
But it does look now like I'm draining the fluid, dropping the pan...inspecting the pan for any evidence of serious failure and go from there...simply can't think of anything else other than the selector module and not really sure how I can test that...would be nice to know if that selector module did fail electronically, wether it would show the trans codes I'm getting, or is there codes specific to that module failing electronically...that would at least tell me whether or not to pursue it.
Will carry on with my paint prep today weather permitting while I await cooler and may have time to drop the pan before work to see what I can find

 

[Steve@Avantgarde]

If the selector module fails in anyway it will either lock in park and you have to use the emergency release or it will not recognise the CAN signal and default to 2nd gear. There is nothing on your selector module that will prevent the vehicle from moving. I could remove your selector module, pull it into drive manually and drive the car where ever i wanted, within reason.

Trust me, you are barking up the wrong tree.

Before fitting that cooler, I would drop the oil out, or you will run filthy old and potentially debris fluid through your new cooler causing you more issues.

I think you need to understand how a gearbox and TC works and delivers power, and then understand how the electronics to the gearbox operate along side that before committing to spending anymore time and potentially money to move forward with your fault.

Look at the evidence after.

1. You said you had gearbox slip in the previous weeks.
2. You have gearbox slipping and impermissible transmission ratio fault codes.
3. No drive.

If you were to do a guided diagnostics on STAR the very first thing it would get you to do is look at the oil level and quality, check the filter for fitment and to correct if necessary.

I get it with other garages as well that bring cars to me, the default position to take is that it is electrical because the ECU has listed some codes, and to jump feet first in without actually checking out the whole system and ignoring basic diagnostics.

 

[Blueyes1971]

Thanks Steve for sticking with it, I really appreciate your input and experience.
I will of course drop the pan next and check for debris evidence and inspect the the valve body and plate.
Also, how do you explain Arudge's experiencing exactly the same issue and then simply turning his vehicle off and on for it to simply clear...it very much suggests his issue at least was / is electronic, and therefore by definition suggests mine could also be.
Cheers

 

[Blueyes1971]

Hi Steve....I also found this in the 722.6 service manual...regarding limp mode and total loss of drive.
The tcm reverts the transmission to neutral with total loss of drive electronically

 

[Steve@Avantgarde]

Thats only if you are driving.

For example, you are in 5th at 70mph and something lets go, it will trigger neutral so as not to lock the back axle and spit you into a spin.

 

[Steve@Avantgarde]

Thanks Steve for sticking with it, I really appreciate your input and experience.
I will of course drop the pan next and check for debris evidence and inspect the the valve body and plate.
Also, how do you explain Arudge's experiencing exactly the same issue and then simply turning his vehicle off and on for it to simply clear...it very much suggests his issue at least was / is electronic, and therefore by definition suggests mine could also be.
Cheers

Probably not a gearbox issue. Who knows without looking at STAR. No one fault will be the same and what will fix one fault won't necessarily fix another, even if the symptoms are the same. Look at the evidence from your vehicle and carry out the diagnosis procedure.

FDC. Fault. Diagnosis. Cure. In that order.

 

[Arudge]

Probably not a gearbox issue. Who knows without looking at STAR. No one fault will be the same and what will fix one fault won't necessarily fix another, even if the symptoms are the same. Look at the evidence from your vehicle and carry out the diagnosis procedure.

FDC. Fault. Diagnosis. Cure. In that order.

We have been on STAR and there was little to report, brake light switch, although i had had no symptoms of brake light switch failure, replaced regardless. Faulty R/H alarm sensor, passenger occupancy sensor, nothing of any real interest. It was the gearbox compensation figures that appeared way out of wack that was the subject of my next line of enquiry.



Thats only if you are driving.

For example, you are in 5th at 70mph and something lets go, it will trigger neutral so as not to lock the back axle and spit you into a spin.

He was driving wasn't he. A steady 50mph when he experienced a surge in revs before dropping to tickover and losing drive.


My problem is different in as much as i have drive, or i would have drive if i could get off tickover. Something is disabling the accelerator pedal and i've yet to find what it is. Currently thoughts are regards the mechanical condition of the transmission. I have purchased another transmission and i'll pull it apart for a full inspection. A subject for another thread.

Steve. Good to see you back by the the way.

 

[Blueyes1971]

I would suggest the trans would spit gears long before it locked the axle resulting in a spin of a 2ton monster at 50mph.
Just my thought on that specific senario .
Thanks again for sticking with it fellas .
I'll drop the pan tomorrow weather permitting and update with my findings

 

[Arudge]

I would suggest the trans would spit gears long before it locked the axle resulting in a spin of a 2ton monster at 50mph.
Just my thought on that specific senario .
Thanks again for sticking with it fellas .
I'll drop the pan tomorrow weather permitting and update with my findings

It doesn't quite work like that mate. As your trundling along, your listening to the radio, your mrs is arguing with your daughter and the dog is chewing the seat belt, your car is collecting an enormous amount of data. At any given time your car knows how fast it is going, it knows how fast each wheel is going, and the camshaft, the crankshaft, the various clutches in the transmission, and compares those values with the map. If something isn't quite right it will make adjustments, fuel trims, transmission compensations. If something is really not right it will shut down.

What Steve is suggesting is that you've suffered a catastrophic failure within the transmission, he's suggesting a split clutch basket, drum or TC failure. Whatever, something is so bad, so far away from what is expected, so far away from the map that the failsafe has kicked in and shut the engine down, and put your transmission into neutral, To stop your engine and transmission being torn apart and launching you in a hedge.

Hopefully you will see some evidence of this in the pan. Don't throw anything away, take lots of pictures.

On the face of it, given the evidence, your transmission has had it.

By your own account, the engine surged, also known as transmission flare, you lost drive. Failsafe engaged, you coast to a halt.

Your transmission hasn't locked up, your not in a hedge, yours mrs is still arguing, the dog is still chewing the seatbelt and your left asking nothing more than WTF? Everybody is still breathing.

Sorry for the drama, I really need my bed!!

 

[Blueyes1971]

I hear ya...but the surge would come anyway after trans has either let go or been shut down or simply jumped to 2nd gear...the surge was result of what happened not part of the happening.
And the lack of any noise what so ever...and I mean like as if I simply shifted to neutral leads me to believe it's not catastrophic...or at least not in the chewing itself apart catastrophic...it was in drive at 50 in cruise and then simply nothing....I'm not saying something in the trans hasn't let go...just if it has, it did it silently.
And if the fail safe is to stop it tearing itself apart then I guess it has done its job...or at least silently.
My comment about saving the car from locking an axle and sending it into a spin was that I see the fail safe stopping that happening as unlikely as a 2 ton truck at 50 would simply send gears out through the casing before a spin of any kind...that's what I'm saying...I'm certainly not dismissing any advice, especially from those more experienced than me....that said I'm no novice...I rebuild engines and restore vehicles and have no issue completely rebuilding the 722.6 if needs be and in fact almost hope I have to...I'm also completely aware of how these work...it's the governing brains behind the show that's generic and non specific a lot of the time in is diagnostic codes..my persistent covering of the bases is simply because the diagnostics on these in my experience is vague at best and have found many opinions especially from Mercedes machanics themselves to be incredibly ambiguous and wrong time and time again.
In short I've dismissed nothing and will follow all advice one step at a time including my own gut feelings and the sound advice reasonings you guys are taking the time to put forward.
I'm sure as a collective we will figure it out.
I will drop the pan tomorrow and see what's lurking in the sediment.
But it would not surprise me at all to find nothing but general wear and tear...we'll see and fingers crossed
Thanks very much again

 

[Arudge]

I hear ya...but

It's good to see you have interest and understanding and i share your sentiment regards the ambiguity of the diagnostics, hence my comment 'there's a lot more going on than what is being reported'.

Sure, i want my car fixed but i also want a full understanding of how it works and what has failed. Steve is very good, he see's a lot of damage and has a technical mind, he's well worth listening to.

I'm in automotive manufacture, a Toolmaker, and arguably responsible for some of the sh!t that Steve has to sort out (sorry Steve) although i'm mostly JLR. I was with the company that was partly responsible for the disaster that was the Range Rover P38 V8 in the nineties, which was wholly avoidable but nobody could be arsed, i see this attitude a lot, even today.

I'm sure as a collective we will figure it out.

I'm sure we will, just keep posting.

 

[Blueyes1971]

It's all good... I truly appreciate both your advice and time... he is my initial findings

 

[Blueyes1971]

No chunks or failure debris as yet... tried to show general wear debris at the magnet .. although there does appear to be a slight burnt smell but not sure if I'm imagining that to be fair... some of the fluid is red and new and other golden but I guess that is where I topped it up (0.5 litre after I towed it home... all I can see is incredibly fine sediment ... will update my findings on opening the filter up as soon as do

 

[Blueyes1971]

More pics while I'm at it