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Discussion Starter #1
Hello all,

I'm having issues with the gearbox, it seems like the limp mode type of thing... But there's something else I need help with. When I move from park to drive (or any other gear) it won't show in the dashboard. I'm assuming the gear you're in should show left side of the clock, right?

What could be causing this issue? I plugged the ODBII reader and I'm only getting a P0715, already ordered the plug to change in the transmission and see if that takes care of that code. But the question remains about the gear not showing in the cluster.

Any help would be appreciated.

Thank you
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,687 Posts
The TCU senses the position of the stick and reports it to the instrument cluster. Probably your TCU is bad - but scan it first. Did you pull back the carpet and equipment bridge and check for red stains where the harness comes through the floor?
 

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Super Moderator UK 2002 SLK320 Blue
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The TCU senses the position of the stick and reports it to the instrument cluster. Probably your TCU is bad - but scan it first. Did you pull back the carpet and equipment bridge and check for red stains where the harness comes through the floor?

You might also find a sticky liquid on the wiring harness too. The culprit is the Pilot Bush that connects to the auto transmission. The o-rings have perished and transmission fluid is wicking up the harness to the TCU.

oil in footwell.jpg


I was lucky, but if you do find fluid in your TCU, you could try cleaning it out with a suitable electrical contact cleaner and a toothbrush (nothing lost as you'd likely be throwing the TCU in the bin anyway)


Good luck.
 

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Discussion Starter #5
You might also find a sticky liquid on the wiring harness too. The culprit is the Pilot Bush that connects to the auto transmission. The o-rings have perished and transmission fluid is wicking up the harness to the TCU.

View attachment 548694


I was lucky, but if you do find fluid in your TCU, you could try cleaning it out with a suitable electrical contact cleaner and a toothbrush (nothing lost as you'd likely be throwing the TCU in the bin anyway)


Good luck.
Thank you, I'm going to check that module tonight and will report back my findings!
 

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Discussion Starter #6
You might also find a sticky liquid on the wiring harness too. The culprit is the Pilot Bush that connects to the auto transmission. The o-rings have perished and transmission fluid is wicking up the harness to the TCU.

View attachment 548694


I was lucky, but if you do find fluid in your TCU, you could try cleaning it out with a suitable electrical contact cleaner and a toothbrush (nothing lost as you'd likely be throwing the TCU in the bin anyway)


Good luck.
Ok. I took the TCU out and I did found oil in the connector. I don’t think it went inside the TCU so that’s good news. I cleaned the connector with electrical cleaner until the oil was out of there. I guess this means the transmission connector will need to be changed as soon as possible. I will wait until tomorrow to plug the TCU back and see if the cluster is showing the gear.

Thank you guys
 

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Discussion Starter #7
I ended up plugging everything back in place. Still nothing in the cluster, I might need to bring the car to the mechanic to plug the computer and diagnose what’s the real issue. Or maybe the tcu is busted.
 

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Premium Member 2001 SLK200K/2001 SLK320
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1,599 Posts
I ended up plugging everything back in place. Still nothing in the cluster, I might need to bring the car to the mechanic to plug the computer and diagnose what’s the real issue. Or maybe the tcu is busted.
I'm not so sure if its not the gear lever assembly or not as that will also you give you a 'no gear' on the dash but as efair says, it's best to get it scanned first.


HTH
 

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Registered 2002 R170 SLK V8 5.0
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2,026 Posts
Hi,

A regular cheap OBD will not scan all Transmission Codes, whoever scans it needs the correct and appropriate equipment to do the job.

There are only a handful of reasons for no Range report in Cluster in order of probability ................

TCU

Shifter

Conductor Plate inside Trans

Wiring

Cluster

Do not bin your old TCU straight away if swapping it out with a replacement, sometimes, despite replacements having identical part numbers they can have the wrong Version Coding, and you will need the old unit to copy and paste the coding using SDS ................................

Do not ask me how I found that out, luckily the "bin men" hadn't emptied it !!

This is the only way to do this unless you go to MB Dealer or Indie with subscription to MB Server !!

You will know if it has wrong coding as it will go into limp mode as soon as it shifts, when you drive it, and come up with "Ratio Error" Code if read on an appropriate machine.

Bin it once you have driven the Car a while and know that all is well :wink:

HTH, Cheers Dave
 

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Discussion Starter #11
Thank you all for the help.

I'm going to take the car "limping" to the Mercedes mechanic (it's close to my house so that's good) and read the codes. Also I'll be ordering the connector for the transmission, the dipstick, and some oil to make sure it's up to the right level.

Hopefully the mechanic can point me in the right direction

Wish me luck.
 

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Super Moderator UK 2002 SLK320 Blue
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2,847 Posts
Thank you all for the help.

I'm going to take the car "limping" to the Mercedes mechanic (it's close to my house so that's good) and read the codes. Also I'll be ordering the connector for the transmission, the dipstick, and some oil to make sure it's up to the right level.

Hopefully the mechanic can point me in the right direction

Wish me luck.
Good luck!


You can clean the loom as best you can. Don't use brake cleaner to clean the loom - it's too strong. Use electrical contact cleaner (and lots of it) to dilute the transmission fluid so that it 'drips' away from the loom and leave kitchen towel in the footwell end to soak up any fluid still in the loom that continues to wick up to the TCU.
 

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Discussion Starter #14
Back from the mechanic.

Long story short I have to change the transmission connector and go from there. At this point is a guessing game. So I have to start there and move forward with the transmission plate if the issue is not fixed. The good news is, the shop had some interior parts I needed for my car... score them for $20.

Will keep you guys posted
 

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Discussion Starter #15
Hello!

The connector arrived and I just changed it.

I put half a quart of oil back into the transmission and turned the car on. I had the engine light on but I waited until the temperature reached 80. Check the oil level and filled the rest of the oil. Went back to the car and the check engine light was off (good news). The shifting is still harsh. I haven't driven the car yet to check if the limp is gone, I hope it is...

If this doesn't work I guess the next step is replace the computer... and if that doesn't work I guess I will have to replace the valve cover in the transmission.


I'll keep the forum updated


PS: Still no gear in the cluster, I'm going to try and clean the pcb there and see how it goes.



Thank you all for the help.
 

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Premium Member
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111 Posts
Hello all,

I'm having issues with the gearbox, it seems like the limp mode type of thing... But there's something else I need help with. When I move from park to drive (or any other gear) it won't show in the dashboard. I'm assuming the gear you're in should show left side of the clock, right?

What could be causing this issue? I plugged the ODBII reader and I'm only getting a P0715, already ordered the plug to change in the transmission and see if that takes care of that code. But the question remains about the gear not showing in the cluster.

Any help would be appreciated.

Thank you
My pre-facelift 1996 does not have that facility, although mine is pre production so may have been on the production cars??

20190810_181022.jpg

I am not sure if that is what you were asking in the highlighted bit of your quote :|
 

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Registered 2002 R170 SLK V8 5.0
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2,026 Posts
Hi,

Before possibly wasting a lot of time and parts money I would want to see the results of a Full Scan and maybe some Data on SDS first.

For example, is your TCU, EGS (Selector Module) and ICM actually communicating with each other ?

You could end up with a lot of frustration, expenditure and a still un fixed Car otherwise :wink:

HTH, Cheers Dave
 
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