2014 E550. Malfunction Code: P278300 - The friction power of the torque converter lockup clutch is too high

During the scanning of my fix with for ESP/ABS/Etc, I finally have a transmission code for my weird HARD shifting - especially in 2nd and 4th gear. Here is the story:

2021: (Covered under extended warranty) Weird shifting in 4th gear and taken to the dealership for diagnosis. The dealer received a code for the torque converter and completed the TSB which required a new torque converter and some sanding down of the shaft. I waited for over a week for the torque converter to come from Germany. Drove it home after they fixed it and 4th gear issue persists along with now a 2nd gear issue. Additionally when I would accelerate aggressively the power shut off and was left like a sitting duck merging on the highway - until the car a second later decides to accelerate slowly. I bring it to the dealership and says its my driving style and they do some tests etc and come back with nothing. I take it home thinking maybe they did a reset for the adaptation, but still the problem exists. I take it back again and I am told that I was missing 2 liters of transmission oil - so they filled it back up. The loss of power went away, but I still have 2nd and 4th hard shifts. I went back and told them to change the valve body and it has to be the solenoids on the transmission that need to be replaced (i specifically told them the torque converter lock up - as that was a problem on my old 2003 E500). However, the dealership and MBUSA said it's my driving style and that they won't spend anymore money on it - and happenstance my warranty expired...

2022-2023: I change the fluid myself a few times and try cleaning out the valve body solenoids - everything looked ok. No codes from the scanner. I give up

2023: I buy a Renntech tune and wow, the power. I figure I can trash on this tranny since it sucks, then replace when it breaks. However, I sometimes get the cut out of power like before and I just leave it up to - oh well.

2024: After scanning for codes for the ABS problem I had, I now get the code above. P278300 - The friction power of the torque converter lockup clutch is too high. Any idea what this means? From my research it brings me back to the TSB originally done on the car. My thoughts lead me toward a bad Lockup clutch solenoid (or sets of solenoids). Even though they look clean, then could just be bad.

Thanks

 

I am biased to cut a break early on for the hard working tranny. The causes for the many ways it shifts poorly are external at first.

Given enough mileage and abuse the :

• clutches,
• bands,
• mesh filters,
• magnetic sensors,
• TCClutch and
• SEALS...

will get beyond useful.

Clutch steels + frictions are not sized to be abused for extended periods.

Converter Clutch:
The TCC has its own complete clutch and it is used with partial lock pressure to guarantee wear and heat. As TCC falls apart it sends metal contaminants down the line.
Perhaps you can swap the converter and get an extension on tranny life.

 

I'd say excess clutch pressure is a bonus, to a point. I wonder how high it is? Perhaps it's high enough to cause your harsh shifts? Kinda doubt it but I don't know how the tranz is setup so I can only speculate.
I call BS on "your driving style" as the excuse. Wth would that have to do with anything unless they expect the fix is for you not to floor it. Like the old joke about the patient that tells the Dr: "It hurts when I do this" Dr says; "Then don't do that"
I doubt it's the solenoids but you could always swap them around to see if it changes which gears have issues. I'd say as long as the clutches don't slip then there are no mechanical issues, which leaves electronics. I hate electronics! It's a wild card that makes everything fail sooo much earlier and sooo much more complicated to figure out when it does. MB is the master at making it as complicated as possible.
I wonder if a trans tune could help fix it? Or perhaps the tranz tuner, the actual tuner that is, who would probably know what the problem is from your description. Engine tuners will make custom tunes, but there's a ton of those people. I think there are only a couple people in the world that can tune our tranz? So my guess is they won't even talk to you, but what to I know...

When you get that power cut, is it a full cut or more like you lost half your power? Then you said it accelerates slowly, but for how long is it stuck like that? I've had mine cut power a few different ways but the one that sounds most like yours is turbos:
If they boost logic faults out it kills the turbos and cuts power in half suddenly, and stays stuck at half power. The reason is the ECU sees too much boost at the wrong time, and the knee jerk reaction is to kill the turbos. It'll be stuck like that until you restart the engine, which is easy to do on the fly if using the key, but Keyless Go won't let me and I have to pull over and stop to do it >:| There won't be a code or anything, at least not for me, so if you can't see the turbo command then your only clue is if it matches what I described.
It's not too much boost period, it's just at a certain rpm and load, which is most sensitive at 2000rpm and <100% load. 100% load is maybe 60% power? So from the slightest throttle above normal cruise to ~60% power is the danger zone. When you floor it it can fault as it transitions through that zone.
With no tune mine only did this to me once. With a tune it's much more likely. It all depends on how the tune was done, plus how much vacuum you have and how fast your turbo solenoid can vent that vacuum, because the vacuum controls boost. Since it triggered on me when stock, plus I can see the data and when it faults out, I can tell you it's right on the verge of faulting out all the time. The ecu gives the turbos all the vacuum it can when steady cruising, then when you give it a little gas it vents most all that vacuum. If it doesn't vent quick enough, poof, fault. If the vacuum is higher to begin with, like mine, it makes it worse. The turbo solenoid is what does the venting, and they are not created equal so it may vent slower and also make it worse. It may not make sense since this is a simple explanation, but the gist is it's close to faulting as-is, and a tune can make it worse. To fix it I adjusted the exhaust cam timing so it makes less boost in that danger zone. It still makes full boost when I want, so no loss.
The other power loss issues I've had are spark retard and the rev limiter, but those recover to full power in a second or two so I'm guessing not your problem.

 

The power cut is a total loss of power, as if the engine turned off. I was thinking a pedal sensor, but no codes.

As an example - imagine you are at the entrance ramp of a busy highway. As you try to merge, you slow down to check the ability to merge in your mirror/turn your head, then have to give the car a good push to get it to speed up to actually merge. When I push it, it basically dies out and you hear a "thump" - but everything is still on - and you are slowly entering the highway at rolling speed LOL. It last for about 1 second then (as my foot is still on the pedal) but the car slowly increase speed as if you are lightly on the gas, but are down almost all the way. Power comes back fully after that.

When they refilled the transmission with additional 2 liters, it mostly went away and I only get it sometimes on full throttle. Again, NO CODES. Even after I've changed the transmission fluid myself, same thing persists. Changed spark plugs and it happened again. Tune or no tune. Again, this started right after when I had my transmission worked on at the dealership for the TSB on the torque converter (never happened to me before that). I've also had the transmission dealer serviced (free) after I bought the car CPO because of a deal they were running (I also got spark plugs done too - sweet deal at the time).

To make an additional point of this being an electrical problem, at least on the shifting, I changed my smaller trunk battery. While I had all the battery power out of the car and then installed the new battery - the transmission shifted PERFECTLY. I was amazed. Then after a few more trips, it went back to 2nd and 4th clunking. So it's either a bad solenoids reading which makes sense because if the lockup is engaged during shifting, shouldn't the shifting be harder?

 

I'm not a saint (although I was born on a saint's day and named after the saint ) I do drive and take care of my cars. I've got my 2003 E500 to 300k Miles with a transmission that was deemed 'toast' by the dealership and other professional transmission places at 110k miles. I persisted and did another full flush on the recommendation of a UK mechanic - and viola, car shifted like new for the next 200k miles! I'm starting to read the Amsoil thread and thinking that might be another route.

Any ideas of changing the solenoids with new ones and if they are plug and play? I saw a video of how to clean them with a magnet and mine looked fine compared to the ones on the video. But not sure the condition internally that could cause the fault. These transmissions are finicky.

 

"reboot perfectly clears the tranny poor shifting issue" - There you go!

Now you can believe me when i say it is external issues that initially cause poor tranny shifts.
You can stop Italian tuning your tranny.


> Short "Limp Mode" Like...
The engine output cutting off under acceleration is a major concern. This clue speaks volume!

Check if this is caused by voltage or fuel pressure.
Inspect both under acceleration.

I vote for.... ALT voltage drops below 12.4V under acceleration.
If this fault is proven then a special quick ALT unplug will fix this and your always-tired-battery swap issues.


SCAN : What other clues does your complete MB scan show? other nearby modules faulted?
🤞