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Unwanted Downshift to manual mode, unable to shift up or down.

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Unwanted Downshift to manual mode, unable to shift up or down.

 
Old 05-30-2019, 07:15 PM
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Unwanted Downshift to manual mode, unable to shift up or down.

I have a transmission question hopefully someone has experience with. My recently purchased 09 SL550 R230 (23K miles) occassionally will downshift on its own into manual mode and stay stuck in 3rd gear. This seems to happen when I am driving along at constant speed around 50. Paddle shifters won't work, pressing the Sport/Comfort/Manual does nothing, and the console shift to +/- is also dead. The only way to get a workable transmission is to stop the car and put into park, and then back into drive. Any advise appreciated.
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Old 05-30-2019, 10:22 PM
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You are in "limp mode". The most common cause of this is a failed speed sensor on the electronic conductor plate inside the transmission. To verify, you need to get codes pulled, but a genric OBDII scanner won't do it - you need one that will pull native MBZ codes from all systems. SDS (Star Diagnosis) is preferred, but iCarsoft i980 or MBII or Autel MD802 Elite and some others can do this, too. If it is a speed sensor, you will need a new conductor plate, which is pretty much a dealer-only job as it requires special coding. Price is usually around $1500.
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Old 05-31-2019, 02:41 PM
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Ran Diagnostics

I actually have the MB II from ICarSoft. I ran diagnostics against the Transmission Control Module and there were no stored DTCs. Is there another module I should check besides TCM?
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Old 05-31-2019, 11:08 PM
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Also check the engine and ESP system. They ca both throw codes that could put you into limp mode. If that fails to provide any better info, get it scanned with SDS.
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Old 06-01-2019, 03:23 PM
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ABS Error

So a scan of ESP gives the following error code: Code 6210 ABS anti-lock braking system control. Would that trigger limp? I am guessing that could be from having the SBC replaced recently.
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Old 06-01-2019, 08:39 PM
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ABS problems can cause limp mode. I thing any ABS issues are covered under the 25-year SBC warranty.
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Old 06-01-2019, 09:41 PM
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Thanks that's helpful. I tried to clear the ABS error 6210, and the MB II won't can't clear it. I drove the car again today to test it, and I had 3 instances of the car randomly dropping down into a lower gear either 4,3, 2 seemingly dependent on the speed which is uncommon to have it happen this much. However, in all circumstances I was able to force it back to drive using the console shift I didn't have to move to park. Now this is where it gets crazy. The (-) paddle shift wouldn't work, and the (+) paddle shift would result in a downshift. The console shift worked fine and would downshift or upshift to drive. I agree this probably going to be a dealer item, but I usually like to know what I am up against before I drop it off.
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Old 06-02-2019, 01:20 PM
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OK, if you are able to change gears with the TouchShift, then this is not limp mode. Limp mode will not clear without a shutdown/restart. Since the paddle shifters are malfunctioning, I wonder if the fault is there. Maybe a problem with the clockspring? If you had SDS, you could check them. Maybe the iCarsoft tool can do that?
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Old 06-02-2019, 01:21 PM
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Rodney your pretty good at this. The ESP/ABS warning light just came on in the left dash, and in the right dash says ESP/ABS not operational. Any idea how to confirm if this is a warranty item?
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Old 06-02-2019, 06:02 PM
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I am all over the place on this issue, but the ESP/ABS has cleared. I can reproduce this failure by disconnecting the battery so I am not sure anymore that these 2 issues are related. I have also confirmed that I cannot reproduce the "limp mode" issue when the consumer battery has a full charge. I have another thread going about my consumer battery losing amperage when sitting idle for a week or two, and I am starting to wonder if a poorly charged consumer battery could be causing the transmission "limp". They sure are correlated. So next step is to resolve the aux battery issue first, and hopefully see if that clears the limp issue. I'm guessing it could be possible that a sensor isn't getting enough or fluctuating voltage resulting in a faulty signal.
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Old 06-02-2019, 11:09 PM
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To verify if it's an SBC warranty issue, you;d need to pull codes. But a weak battery can cause all sorts of odd problems, so sort that our first.
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Old 06-10-2019, 10:32 PM
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The downshifts are back with a vengeance. The battery issue is resolved so the picture is a little more clear.

It usually happens after 15 to 20 minutes of driving. It will shift, on its own, to first, second, third or fourth depending on speed. Most of the time I can shift my way back to drive, other times it appears to be in limp and I have to park it. After clearing the issue by upshifting to drive or parking the car it often happens again almost immediately. I cleared codes before I drove it, rechecked after the failure and found nothing I checked every module.

Any ideas to further diagnose are welcome. For me a dealer STARS scan is a last resort but so far that's looking like the best option.

Last edited by ceberus; 06-10-2019 at 10:36 PM.
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Old 06-11-2019, 03:31 PM
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STARS SCAN RESULTS

I took the car in for a STARS scan to determine why transmission is randomly downshifting to various gears. The result has left me even more baffled == passenger side SAM under the hood is non-repsonsive and needs to be replaced. The mechanic said STARS can't scan deeper until this module is fixed.

He thinks this could cause the transmission issue, but after describing issues with the paddle shifters he thinks it could be Transmission Condule Module (TCM) or a Shift Module.

My ICarsoft doesn't report any issue with the TCM. So I have 2 questions if any can answer:

1. It seems like a stretch to think the passenger SAM could be the issue. Further, why would the passenger side SAM impede communication with the TCM? Will replacing have any chance of changing anything? Wouldn't I see other electrical issues with a bad SAM?

2. Dealer says cost is $900. I've read DYI is possible has anyone replaced one of these before? It doesn't seem too difficult and I don't believe it requires coding. I might just buy a rebuild or send mine for rebuild and install it myself. But again, I am skeptical this is going to change anything.

Thanks.

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Old 06-11-2019, 09:58 PM
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I think it's very possible that the right side SAM is at play here. One of the things that is fuses is the gearshift.
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Old 06-11-2019, 10:21 PM
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That's great news to hear I just read article SAM can cause limp mode when it fails and I was wondering how.

I just checked the module with icarsoft and it cant even read it just crashes the scanner. Drivers side sam reports no communication tho.

Already called dealer to repair, thanks I agree I think sam is culprit here I wish I had paid more attention to this module on the initial scan.
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Old 06-12-2019, 09:54 AM
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Originally Posted by ceberus View Post
Dealer says cost is $900. I've read DYI is possible has anyone replaced one of these before?
Replacing a SAM takes about 10 minutes and requires only a screwdriver or other implement to pry the SAM apart from its fuse box. On a c. 2005 or newer car a replacement needs to be programmed with a Software Calibration Number (SCN), I believe. (Rodney and others know more about this than I do).

There may be hacks to get around the need for obtaining an SCN from a dealer or other professional service -- I don't know -- it's been thoroughly discussed on the mhhauto.com forums.

There are services which will provide an SCN for a one-time fee. Here is one doing business on aliexpress.com which charges $34 per session: https://www.aliexpress.com/item/Onli...881832045.html.

Originally Posted by ceberus View Post
...I wish I had paid more attention to this module on the initial scan.
A drawback of the iCarsoft 980 and perhaps your MB II as well is that you have to address and then query each module individually to check for faults. In a particular case where one is unsure what systems may have a role in a problem being diagnosed, reading codes from as many as 30-odd modules can be tedious and time consuming. In contrast Star Diagnosis automates all of this via its "Quick test" and presents a concise summary of the results.
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Old 06-12-2019, 10:55 PM
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I just poked around in SDS "simulation" mode and I do not see any SCN coding for the front SAMs. Of course "simulation" mode is not 100% the same as live mode, but usually it does show when SCN coding is needed. Also, the front right SAM on a MY2009+ facelift car only has two settings: HID headlights and curve illumination lamps. I think all USA models cam standard with these, so a used SAM from a MY2009+ car should be a drop-in replacement needing no coding.
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Old 06-13-2019, 09:24 PM
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Thanks Rodney. I already scheduled with dealer for Tuesday the cost is $760 they gave me credit for the STARS scan. I decided to let them do it because I met the mechanic and he talked with me for 20 minutes and i learned a lot. He will also rescan after the SAM install to check the transmission and shift modules. I like the mechanic for me he's adding value so it's worth it.

New trunk battery also drained again this time while on the tender. I think its SAM related. So the direction I'm heading now is that SAM is entire problem causing both battery and shifting failure. Can't wait to fix it!
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Old 06-15-2019, 06:38 PM
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Can anyone describe the location of the passenger side SAM for an SL550? I'm guessing engine compartment battery needs to be removed because I don't see anything else obvious.
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Old 06-19-2019, 08:57 AM
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For anyone following this thread, the solution to this issue was somewhat complex. After the dealer replaced the passenger SAM module, the SBC which they had replaced last month began reporting short to ground on SDS and dash lights popped up. The MB mechanic thinks the SBC was affecting speed sensors and they plan to replace the entire SBC, again. This actually makes sense, since the issue began immediately after they replaced the SBC. Also, I am glad I had the dealer replace the SAM it required coding.
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Old 06-19-2019, 11:25 PM
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Of course SBC is now covered under a 25-year warranty, so don't let them charge you for that!
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Old 06-26-2019, 10:03 PM
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The SBC is now fixed, the SAM is fixed, the sensors are fixed. No more errors. STARS says everything is fine. Eager to drive the car, I drove 300 feet and the ghost living in my transmission began downshifting. The service manager said it could be the paddle shifters causing the issue. He checked the historical STARS report from his desk PC for the steering module, but it was fine. However, I found this link on another forum and the symptoms are a direct hit. The description is 100.000% in line with what I experienced. And for icing on the cake the -- year, make & model are exact.

https://www.benzworld.org/forums/r23...ownshifts.html

I'm so confident it's the steering module that I'm done troubleshooting. I'm going to instruct dealer to just replace it. If anyone can provide the Part # for 2009 550SL that would be great so I make sure the right module gets done. If DIY makes sense let me know. Thanks in advance.

Last edited by ceberus; 06-26-2019 at 10:08 PM.
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Old 07-12-2019, 07:22 PM
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Just to follow up for anyone else who might see this issue the ultimate cause of the unexpected downshifts while cruising along was the steering column module. Replacing it fixed the problem. An unrelated issue was passenger SAM failure. The MB dealer was unable to run star diagnostics until that was fixed. Even after SAM was replaced, there were NO ERROR codes indicating the steering module was at fault. I took a calculated risk and replaced it based on a post I found on BENZ WORLD . To recap symptoms:

1. Car downshifts at random, this could be because the steering module thinks it's getting a signal (false) from the down shift paddle.
2. When the problem occurs, using the upshift paddle causes a downshift. The downshift paddle is not operational.
3. The console shift will usually work and get you back to drive, but not always. Sometimes you have to stop and go to Park.

This was a tough one to figure out, I got lucky stumbling on an old post.
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