bb85

Good evening everyone, I’ve had a renntech HHT on my 19 E63s for several months now and today I experienced my first issue. While driving on the freeway (in comfort mode) the car suddenly lost power, the dash messages read(I think); rear differential in operational, esc in-operational. The cars rpms were hovering around 1k and the gas peddle was not responding. Lucky I was able to get to the shoulder safely. I turned the car off then back on and everything was fine, I was hoping someone has some experience with this or a suggestion, Car has no other mods just the stage 1 HHT purchased from Renntech. The car has been reflashed and is driving just fine. Any help would be great thank you.

jkob5

I have heard of several tuned cars doing this. Particularly in comfort mode and on the highway. This is the first I personally have heard of a Renntech car doing this, I know of 2 EC cars that do it personally.

shardul

iTrader: (1)

Was your cruise control on?

bb85

no it was not on.

S63AMG888

iTrader: (3)

Spark plugs? I have read on the W212 E63s having that issue with spark plugs. Colder plugs?

shardul

iTrader: (1)

The symptoms you describe have happened on stock cars when cruise control is on. Apparently there is a SW update for it.

Meeru

I have had this issue for a while now. Went into MB dealership and they replaced the rear diff cap.
Drove for a few days and the problem came again, the dealership then replaced the whole diff!!
Drove again for a few days, the problem is back, the software was updated..
Drove again same day.. same message popped back.

Here’s why its happening and I have avoided the message coming back again for the past 2 weeks.
When you drive on the highway around 120-160km/h in comfort and remove your foot off the gas, the “glide” or sailboat icon appears where it shuts the gears off, when you put your foot back on, the rear diff error pops back, you could almost feel the teeth of the rear diff finding it hard to engage.

Solution?
Have renntech disable your “start/stop” feature which they can do, you will not face this issue again. I turned mine off manually and the issue has not repeat itself.

IMHO, I find it utterly useless that due to north american requirements, these german v8s have to add these features in! Best of luck!

internet

Speaking from experience, this is inaccurate.

MuffinFlavored

Hmm... there's no way these cars can update themselves over the air, right?

I don't have the exact issue you do, but my car was tuned for a while using what I'm guessing is the same as Renntech's hand-held-tuner (which I'm guessing is MyGenius?) and it was fine for months.

Now all of a sudden, I get that "rear diff inoperational" message too randomly. Sometimes I get it, sometimes I don't. I haven't found the root cause yet...

Wolfman

Perhaps unrelated but I have seen the same message pop-up occasionally since new with zero impact to the behavior of the car. Car is stock and it never dislayed past a restart. I just consider it a random nuisance message tripped by software, not sensors...

mercshepherd

I installed a Renntech Tune on my 2012 CLS550 with the hand held tuner. Biturbo V8
Driving at WOT the car would randomly lose significant power and go into limp home mode.

I would have to stop the car, shut off and restart, and things were back to normal.

Also at very high speeds around 95 to 100 mph at WOT the car always lost power suddenly at the exact same speed.

I data logged turbo pressures, and other parameters and could not find any obvious cause.
I worked with the renntech tuning engineer, and finally he suggested I check the version of the Mercedes ECU programming

It happened to be an older version as it was never updated by a dealership. And the Renntech tune was done on much newer versions of the Mercedes ECU programming

The solution was to update my car's ECU programming to the most up to date version. The sudden loss of power incidents stopped happening.

Although occasionally when doing WOT at highway speeds there is a violent jerk as if the engine briefly shuts down and back on again. Very worrying. Rare occurrence but it should never happen

These renntech tunes are NO WHERE NEAR PERFECT. Renntech has very limited staff, knowledge and resources to work all the bugs out of a tune compared to an Auto Manufacturer like Mercedes who has almost unlimited resources to fine tune the engine and transmission calibrations. There are probably dozens of Mercedes engineers working on just the programming/ of the engine control unit and getting the "tuning" right.
Compared to a handful of people working on a tune at renntech

David Bogle

i have had this, and it turned out it was a bad gas pedal, well the position sensor in the pedal. there is a recall on this for certain cars.

mercshepherd

The Limp Home Mode, And the engine cutting out never happened before the Renntech Tune.
So I dont think its the gas pedal position sensor in my case

uberwag

A little late to this but have the same problem. With RENNtech tune in comfort on highway, it’ll go to limp mode after 20-30 minutes. Coast to shoulder, turn off, turn on, resets. When flashed back to stock, never ever ever has happened. When on the RENNtech tune and in anything other than comfort (sport/sport plus/race/individual set up to sport with comfort suspension), it doesn’t happen. Asked RENNtech and they said they hadn’t heard of that issue (but the previous owner who had it tuned specifically brought it up). Not sure if there’s a fix or not, I’ve just been stuck driving in stock ecu mode to make sure it doesn’t happen on accident with someone else driving or when there’s traffic. Now that I’m out of warranty anyway I’m switching tunes. Was super surprised renntech had this issue-they are supposed to be the ones who err on the side of drivability/OEM-ness.

mercshepherd

My solution was to update my engine calibration to match the renntech tune properly. If that doesn't work. DEMAND YOUR MONEY BACK FROM RENNTECH. Talk and email the tuning engineer directly. Not the salesman. Let us know what happens

uberwag

Wasn’t my money-bought the wagon with the RENNtech tune on it. Did have all the calibrations updated months ago from Merc to see if that would correct it-no dice. Glad that worked for you though. I did email RENNtech again to give them benefit of the doubt, but 1) I realize I’m not their original customer so they don’t need to work hard for me, and 2) I don’t know if I’d trust a fixed tune or would want to mess with it to test it out. Lost confidence, etc.
I’ve had a RENNtech tuned car before and it wasn’t problematic at all, so this is an outlier, but wanted to share feedback on here. I think I’ll get a fresh start with a different ecu tune to go with a cpc/tcu tune and have started asking around to the other shops I’ve used before (eurocharged, ECC, etc)

uberwag

Update-got a CPC tune, and tried the RENNtech tune again…still broken. With the RENNtech tune, on the highway at steady speeds in comfort mode, goes into limp mode and everything shuts down. Glad I could make it to the shoulder. Goes away after a restart, but I was hoping that after getting a CPC tune that maybe that would have resolved it. Alas. Will definitely be getting a tune from a different vendor - this is wild, have never had an experience like this with a ‘premium’ stage 1 tune. Here is a video of it once I pulled over and put it in park. Revs bouncing, all the error messages, no throttle input allowed.