Good afternoon beautiful people of the forums. I recently purchased a 2000 S500 with 150k miles. I went into the purchase knowing that the transmission had problems. The car would be in limp mode unless it was warm, then it would shift perfectly. I also noticed the torque converter shuttered in any gear in higher RPM, but that wasn't too concerning to me because I knew the fluid needed to be changed. Another note is that the dipstick tube cap was missing, which I later found at the bottom of the plastic covers on the bottom of the car. These transmission issues were not tripping a check engine light or any OBD codes.

Fast forward to when we start working on the car, the first thing we did was unplug the pilot bushing/ 13 pin electrical connector to the conductor plate. To my pleasure (at the time at least) it was soaked with oil. We cleaned the connections and replaced it with an OEM Mercedes Electrical Socket. We tried the previous procedure of warming up the car and driving it, but it was stuck in limp mode, which was strange. Why would it get worse with a new pilot bushing?

To try to resolve the torque converter shutter, we drained oil out of the transmission pan plug (did not remove pan) which dropped about 3 quarts. We filled up what came out with Valvoline Maxlife ATF and double checked with our transmission dipstick. After the car was warm after checking the fluid level, the car shifted, Hooray! Drove well and the shudder was slightly improving.

(Note: The old oil (the stuff we drained out) was very thick and looked more like motor oil than transmission fluid, but there were no metal pieces at all.)

The next morning comes around, it starts in limp mode, which is still a little bit confusing, but I was expecting it to at least start working when warm. Which didn't happen. This left me very confused, but we repeated the process of drain and fill again a day later. The exact same thing happens. Drain 3 quarts out, put the same back in. Car works for the night, then next morning, it doesn't want to get out of limp mode, again.

I purchased an iCarsoft MB V2 to read the codes of the TCM and ESM. The TCM only had codes 034 and 130. The ESM had P1856. Which I thought were all related to the gear lever being stuck when trying to shift back to park from N or D. I tried to clear the codes and see if it would fix it, nope. Still stuck in limp mode. I tried disconnecting and reconnecting the battery. Nope, still the same outcome, limp mode.
I then located and removed the TCM to inspect it for oil. There was only a tiny bit of oil on the prongs of the TCM. Nothing crazy like other people having like a quarter of a liter pour out of the damn thing. Just a sliver of oil on the prongs.. I sprayed it multiple times with electrical cleaner and put it back in. Alas, limp mode again.
(NOTE: When I shook the TCM I heard a very slight and subtle rattle. I have a few other 722.6 TCMs for my other Mercs but I haven't checked if they make similar noises yet.)

We measured the oil level again but with the accuracy of the iCarsoft temperature reading. Which was on the minimum reading, so we added a little bit more oil, but of course, limp mode again.

I noticed in the last test drive the trans was whining or humming a little bit, so I knew we had to change the filter.

Next day comes (last night) and we drain the trans oil from the pan and replaced the filter. We get about 4 & 3/4 quart of oil out. All replaced with Valvoline Maxlife ATF. I noticed the color was slowly improving, but was still dark. I put the pan back together and started the car. Of course in limp mode, but it worked after it warmed up, just like the last two times we drained the fluid. But I noticed that after I let the car rest, It was still working. I knew this because of the shift position indicator next to the clock. It would only appear if it wasn't in limp mode and it was relaying the correct information when I changed gears and shift modes. It still worked even 4 hours after of me driving it, which I found miraculous, so I was hopeful that the dreaded limp mode would be gone.

This morning, I try to drive the car just like I do every time a day after a trans oil change. It refuses to leave limp mode. I drive it, shift it through P R N D ( with having to turn off the car to get back to P and R). Still stuck. I check the temperature of the oil with my computer and it is most definitely warm.

I thought fixing this limp mode would be easy peazy after all the knowledge and experiences we have had on our W163, but here I am crawling back to the forums again.

Here are some notes that I want to make sure are clear.

Summary

I have a 722.6 dipstick that I measured with accurately with the aid of the iCarsoft temperature reading while reading the TCM data.

The iCarsoft would pull codes 034 and 130 (Historic for both) from the TCM and P1856 (Active) for the ESM. I cleared both modules, but when I read the codes they are still there. When I try to reclear them it "clears" it quickly, but when I go back to read them, they are still there.

Each time we changed the fluid (in the nighttime) the car would shift and work fine that night, progressively improving how fast it would get out of limp mode. But in the next morning when I try to drive the car again, it will not get out of limp mode no matter what I try to do. It did exactly this each of the three times we changed the fluid.

This morning after the third fluid change when we turned on the car, I saw the gear selector indicator on the instrument cluster, but it only worked for a second. When I would restart the car it would not appear again.

The transmission whine/hum was gone after changing the filter. The shudder still exists but is progressively improving with more fluid changes.

When I was shaking and tapping the old transmission filter, some metal shavings came out, but nothing out of the normal.

I cleaned and put the dipstick cover back on after the first change (without the O-ring because it doesn't fit anymore).

Something extremely fascinating is that when the car is in limp mode, the Pneumatic soft close doors and trunk do NOT work. When the car was out of limp mode, it worked perfectly. How in the hell are these two systems related to each other??

Other problems with the car that aren't directly related are that the B1S1 Oxygen sensor needs replacing because of a heater circuit, the driver front strut needs replacing, (sinks after about 8-12 hours.) then the entire car sinks to the ground (36-48 hours) which I am assuming is an airmatic valve body. Lastly, the blower does not work at all. I do not suspect any of these things to be the cause of the limp mode, but with what I saw with the pneumatic doors and trunk, I am leaving nothing off of the table.

What could be causing the car to only work when warm? Or in my case now, not at all? I noticed there is some play in the mechanical movements of the shifter, so I would assume it would need a shift bushing. I ran into this same issue on my W163 but the shift linkage system looks different and might call for a different bushing, but that doesn't explain why it previously only worked when warm. I would assume that there would be a problem with the shift module, but again, how did it work when it was warm, I would assume that temperature wouldn't mess with the shifter at all. It doesn't look like anything was spilled in there either, it still has the cover which is clean.

It almost seems as if this car only wants to work in the nightime or something. Im gonna try later to see if it will magically work, but I have lost hope and I am genuinely lost and confused now. Its like this car has some sort of demon that wants to haunt me lol. Please don't hesitate to ask me any questions and I thank you in advance.

 

You probably have an electrical problem if the transmission dash display cuts off at the same time the pse system
fails

start by checking and cleaning each and every fuse block and SAM for corrosion

 

I have looked already but I didn't see anything obvious, might check again.

I went out to the car a couple hours ago to check if the shift indicator light would come on when I put the key in the ON position, which of course didn't display anything. When I closed the door the PSE worked. So it seems that PSE can work in limp mode, but when it doesn't work the car is in limp mode. Weird machines these cars are I tell you

 

https://mbworld.org/forums/e-class-w...ode-p1856.html

ESM faults do not play well with your transmission. Above link is from the 211 section, but same idea. Better detail on a w203 post I'll link below

https://mbworld.org/forums/c-class-w...rse-shift.html

 

Is P1856 a definitive code for a bad gear selector? Or could it be a code that is just supplementary to the root issue of the limp mode. I am planning to grab a shifter from the junkyard, already went through this with a W163 but didn't have MB2 at the time.

 

Look in the right SAM under the hood and find the TCM (Transmission Control Module), a small black plastic box. Carefully open the box and thoroughly wash the electronics with brake cleaner spray or similar. Reinstall and see if that helps.

 

The code tells you that the position detection function has failed. May be intermittent and change with ambient temperature (it gets pretty warm down in that area when the car runs/drives). I would not go any further with transmission repairs until the ESM fault is rectified. I had a w203 that would slip taking up drive when shifting from park with NO dtcs in transmission or ESM. Got "tunnel vision" on the tranny and wasted a bunch of time and effort before dropping $35 for a junkyard ESM that fixed the problem immediately

Not second guessing Wally's suggestion on the TCM (free to look, and also a common problem), just sharing a similar experience

 

Thank you for this info!! Im definitely grabbing a TCM and a shift module when I go to the junkyard next time. Cheers and Merry Christmas!