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S500 Stuck in Limp Mode

6K views 27 replies 8 participants last post by  Spudnik 
#1 ·
Hi All

My 2004 S500 L is stuck in limp mode. I've had limp mode on and off before, but it normally always goes away when I stop and restart. I've had the ECU codes read for other problems, but they never picked anything up that would suggest a problem with transmission.

The car's transmission has behaved oddly over the last few months. As well as limp mode, sometimes it would get stuck in 3rd or 4th gear and not shift either up or down and could not be overridden by using the manual option by knocking the gear shift left and right.

Pre-save inactive message appears on the dash after about 30 seconds of starting. I've tried to get rid of this message by turning the steering lock to lock. I've also disconnected the battery for 10 minutes. I tried to check the transmission fluid, but I don't have the tools and I also couldn't really see anything obvious under the bonnet. Not sure if this car has the the 7G or 5G transmission. I thought I spotted some fluid on the drive, but it was difficult to tell - maybe a transmission fluid leak.

I did check around the forums and tried the easy fixes, but am stuck now.

Any ideas of what to check next? I would take it to the local indie, but he's at least 10 miles away and I'm not sure the car will make it.

Thanks,
Spud
 
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#3 ·
Hello - I didn't use anything to scan the codes. It doesn't go and won't get out of first or second gear, so I'm assuming it's in limp mode. I don't have an SDS or system to plug in to read codes. I will need to to take it to a mechanic, but I was trying to see if there was a way to get it out of limp mode so I can drive there.
 
#4 ·
One possible cause is the common problem where a leaking transmission electrical connector allows ATF (Automatic Transmission Fluid) to wick up the attached wire harness and into the TCM (Transmission Control Module). The ATF can cause random problems with the TCM. Cleaning the TCM is an easy DIY job. Might or might not fix your problem, but it's easy, cheap, and often helps...

Purchase a spray can of good quality "Brake and Parts Cleaner". Open the right under-hood SAM (Signal Acquisition Module), the lidded black plastic fuse/relay/control box that is located at the back of the engine compartment under the right corner of the windshield. Carefully examine each of the wire harnesses at the top of the box for any traces of oil on the wires. Gently tug the oily harness up and out of the box, bringing the attached TCM with it. Unplug the TCM, and open it, being careful to avoid breaking the plastic latches. Use the parts cleaner to remove all traces of ATF, and let the box dry completely. Reassemble and reinstall. Drive the car a few times to see if this fixed the problem.

Changing the leaking connector is fairly easy, but does require getting under the car. The part is available on-line or at your Mercedes or Dodge dealer, and is usually less than $20. Replacing the connector usually causes only a very, very small loss of ATF during the process. If you don't change the connector, you might have to clean the TCM every five or ten years.
 
#5 ·
Hi WallP

Thanks for the very clear instructions. I opened up the lid of the box and everything looks pretty clean. No traces of oil or wetness on any of the leads. It looked non trivial to pull the wiring harnesses up through the box as they were fixed to the sides and taped. I decided to leave it given they looked clean.

I'm now charging the battery as it was completely dead a couple of weeks ago and I'm wondering if its not giving enough volts.
 
#6 ·
Just to make sure -

All references to left/right on a vehicle are based upon the viewpoint of the driver seated in the driving position. This means that when you open the bonnet and are standing at the front bumper looking into the engine compartment, the right SAM is on your left...

The wire harness for the TCU is not normally attached to the side of the SAM, nor is it usually taped or fastened down.
 
#8 ·
The car's transmission has behaved oddly over the last few months. As well as limp mode, sometimes it would get stuck in 3rd or 4th gear and not shift either up or down and could not be overridden by using the manual option by knocking the gear shift left and right.
One thing I do not understand is, if you are having problems for the last few months, why wait till it completely goes into limp mode?? Why don't you try to fix it and get to the problem while is still drive-able??

I would listen to Wally and check that electrical connector first.
 
#9 ·
Yup, I did that. Paid £200 for a crank shaft position sensor and the fitting, which I was told would cure the other problem. Guess what, it didn't. So no I didn't wait until an utter fail, I've been trying to sort it for a while. I should have mentioned that, but I didn't want to pollute the troubleshooting with stuff that was already done.
 
#12 ·
So you have been having troubles with the transmission going into a limp mode and your mechanic changed the Crank Sensor?? I would run, run far away from that mechanic. If you have seen puddles of tranny oil on the ground that may indicate that you are low hence the car going into the limp mode. I would order a Tranny deep stick from ebay or even your Mercedes Dealer since they are not that expensive and check it first before you bring it anywhere. Do not attempt driving it since you risk blowing the tranny.
 
#10 ·
So I opened the right lid this time. Again everything seemed pretty dry. I tried to pull the wiring harnesses up out the box, but they seemed quite well fixed. Also looks like someone was there before as there is electrical tape on some of the wiring and around the hose. Doesn't look sinister, maybe just keeping things together and tidy.

When I lifted up certain cables, it felt like I could detach the entire fuse board on the left side of the box, but I thought better of doing that. I'm going to see if I can get the local indie to take a look tomorrow or advise how to get it the 10 miles or so it needs to go.
 
#11 ·
Hi,

If it needs it then a Tow Truck for 10 miles will be significantly cheaper than rectifying a barbecued Auto Trans :wink

There are 2 forms of Limp on MB Transmissions, "Soft Limp" which will be a minor fault and will reset with Key Off / Key On cycle, and then there is "Hard Limp" which will not reset with anything other than a very decent Diagnostic Machine / SDS Machine.

Make certain whoever you let work on your Car has SDS, not "xyz", because anyone who is a decent and good MB Indie should have it, if not they are not serious contenders to do a decent job at a sensible cost, in other words they will be part of the "chuck expensive parts at it until it's fixed, (parts darts), brigade" :frown

HTH,
 
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#13 ·
Hi Dave

Thanks for weighing in on this one. I managed to get the car over to the garage, different place than before. They seemed to be suggesting the same things about wiring harness and leaking into the plastic box under the bonnet that WallyP mentioned. These guys are ex MB main dealer mechanics, I saw all the certificates on the wall, so I suppose they know what they're doing. They don't use SDS though, they have Auto Logics which can send data back to a central system and if needs be an MB tech can look it against all other data logged. I guess it's useful.

I'll report back when they have diagnosed it.

Spud

PS. They are so many ads on this site now, the page won't sit still to type the reply :(
It's better once you login.
 
#14 ·
Hi,

Autologic will be fine, that is a very expensive piece of kit that actually will do all that the Main Dealers SDS can do Diagnosis wise ...............

Last time I looked at that it was on a par with the other "Big Guns" for large independent multi manufacturer Garage Workshops ....................

Circa £20k for the unit and 2 vehicle manufacturers softwares, and then another £9k per additional manufacturer s/w :eek

Sounds like you've found a good indie there :wink

As for the adverts, that is way above my pay grade, and it may possibly be more to do with your device / browser :dunno:

Cheers
 
#16 ·
Ok so the results are in. Received a call from the mechanic and it's bad news. The electrical plate or something in the gear box, back of the gear box needs to be replaced. Because all the electrics stuff is on there and it includes the anti-theft system, either only MB dealer can service it, or they need to take the whole control unit thing out and send it away. Apparently, this saves recoding the whole thing when it is reinstalled. Total cost - about £800 - £850. May also need a new battery and the gearbox mounts are shot, but they're covering that in the costs.

What do you guys think. Do you know what the electrical plate is?

Spud.
 
#17 ·
Hmm...sounds like the conductor plate, possibly the speed sensor (common failure item on both fiv-speeds and seven-speeds). Unless your car is a 4Matic, your 2004 S500 has the 7-speed, specifically the 722.9 transmission. M-B decided, for no good reason other than forcing you to go to the dealer, to make the transmission part of the "Theft-Relevant Parts" list, starting with the 722.9. Were it the 722.6 (five-speed, the immediate predecessor), you could do it yourself; I have, on several 722.6-equipped cars. But now you have to have the mothership program the conductor plate to your vehicle's VIN, and you can only buy "Theft-Relevant Parts" from the dealership. Sucks, huh?

That's why I avoid the 7-speed like the Bubonic Plague. M-B purposefully made it less DIY-friendly.

The 5-speed (722.6) suffers no such brain-dead nonsense.
 
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#21 ·
Hi,

If only it were that easy .....................

That procedure requires one to have a paid subscription to MB Server, (around £10,000.00 last time I looked), as does all SCN Coding.

Vediamo can do this, but only if you can get the correct files from Database.

Far easier to get it done by a Transmission Specialist who can do this procedure. They will virgin the unit at the same time.

HTH,
 
#24 ·
Hi @johnksss ,

Thanks for your input here, it is all valuable knowledge for most and I'm certainly not trying to 'P' on anyones parade :wink

I used to own a Transmission Shop, we used to do at least one 722.9 Mechatronic VB per week, I fully understand the procedure ;)

These 722.9 VB Modules definitely need ONline SCN Coding, even the link you put up says that.
I have a feeling it is easier to get access to MB Server in USA than it is in UK, due to different laws on access to software etc

I have the very Machine that @Paul600600 mentions as well as my original C3 / Win XP one, and yes on the 64 bit Win 7 C4, via a 3rd party who does pay the on line subscription it can be done.

Fact is the clone SDS that most owners have will not do this as MB Server will not recognise these units !!

TBH since I sold up the Tranny firm and re located, unless it is a Mercedes 722.6 I do not get involved with Auto Trannys these days, there is plenty of good paying work out there that does not give so many headaches :wink

HTH,
 
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#25 ·
Nothing wrong with that at all! :)

How long ago was that?

That's if you do not already know how to get the original SCN information from the original or how to Virginize a used one or And of course the simple way. Buy one already virginized or new. Vediamo 5.0 also comes to mine. AVDI is another one. Also, side note....Xentry is not the one doing the offline SCN coding, it is DAS. And has to be done as a standalone. After like 2015 things get a bit harder to do offline programming and SCN coding. Also found out that they started putting spyware in the software so there is that as well. 2019 version of Xentry you can pretty much forget any ideas of doing it offline. (For now anyway)

That is also a good possibility, but then there are ways to get past that if one doesn't want to black list their said unit....

But I'm in no way shape or form an expert at this. Still in the trial and error phases after 5 years of tinkering and getting things to work. :) Then come in the forums looking for answers or possibilities I had not even considered before. So a big thank you to all involved! Or share some ideas I have picked up along the way....
 
#26 ·
Hi @johnksss ,

I sold up my share of the Trans Firm back in 2004, then carried on working there part time with my business partner, (who bought me out), until 2006 when we relocated to NW Scotland, so yes, I can understand that aftermarket Technology has moved on since then :wink

I do visit them when we are down south visiting relatives etc, and they are just buying in Rebuilt and Virginised / SCN Coded Valve Blocks from a specialist, get no trouble and all in all it is the easiest way for them.

Out of curiosity, does this apply to SCN Coding of other control units on cars up to the 2015 era ??

If so I'd be very interested in learning more, especially where to get the SCN files and what / where exactly to add them to DAS .........................

PM me if your prepared to disclose anything but you would rather do this off forum, or I'll even pm you my EMail :wink

Maybe I just need to invest in some different kit ;) :dunno:

Cheers Dave
 
#28 ·
Hi All

So the final bill is in. Not bad I suppose - total just over £850:

TCU repair with postage to send away was £250
Labour and Diag £300
Rest was £300 of odd an sods - Transmission oil, filters, seals, plugs, quite a lot on bolts, plus a new gearbox mounting and brake light switch.
 
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