Wob1234

Hi I am new to this forum. I joined because I was hoping you could guide me where my MB service centre has failed to solve.

On approx one trip in ten my 2018 CLS350D 4matic goes into a controlled drive mode. It disables the manual paddle shifters so that M mode can't be selected. Then it changes gear to manage the engine and keep it between 2 & 3 thousand revs. If the speed is slow it pushes down the gear to get it over 2 thousand revs and it won't change up until the revs rise to 3 thousand revs. This means that even at 130km/hr it drives in D6 gear while normally it would be in the highest D9 @ 100km/hr

There are no messages showing and when the car has been checked in the service centre on the computer there are no problems flagged.

The fact that the problem is intermittent is even more annoying. I have had to take photos of the dashboard to show the service centre.

any diagnosis or solution?

Matthew Cronin

WOB1234,
Man I tell you if your car wasn't a diesel I wouldn't say this but it sounds like to me your car MAY be going through a exhaust system regeneration cycle to burn off stuff from the exhaust collector. You aren't loosing speed control over the vehicle in the sense that it still does the speed you want but it chooses the gears/revs and kicks out the paddle shifter etc. I had a 11 VW Toureq TDI with a 3.0 diesel and it would alter shift programing, less dramatically to keep the engine rpm up, create heat so the pipe and collector temps would rise and burn off the particulate. The fact that you said about every 10 rides makes me VERY suspicious this may be the case and in essence normal and part of the cleaning cycle to remain emissions compliant. I will say two things regarding my car. When it went into regen there was a little yellow icon on the dash that would indicate such. The second is if I wasn't going to fast and cracked the window I could smell the paraffins burning off...smells like a unscented candle...hot waxy smell.
So do me a favor and look into exhaust regeneration in your manual and let me know. I am officially curious and highly suspicious this may be it. Matt

Matthew Cronin

Wob1234,
So did a bit of digging last night and found that it is likely there IS NOT a indicator light that signals exhaust regeneration like my older VW's so no visual prompt that its happening. I will tell you that if you go to the dealer either after the next event or you clearly recall the date it happened last it will be logged in the computer. The main thing here is that its not a trouble code so you would never see it there. If it is what I think its the car doing its self initiated maintenance, typically mileage based (could vary and be adaptive based on how you are driving the care depending on how intuitive the software is). For sure the next time it happens if you swing into the dealer and ask them if they can see a regen cycle in the cars logs it will be there if it is.
Like you I am itching to know lol. You want to make sure the car is right and I love tinkering with my head with a good mystery. Good luck and NICE car btw. Matt

Wob1234

Thanks very much for your theory Matt and your interest. Interestingly the service manager in the Service Centre also speculated it might be this but couldn't find a trace when he put it on the computer.

I will take your advice though and if it occurs again close to the centre (which is on my commute) I will drop in and leave it running for them to test. The mode continues at least until the car's ignition is switched off and often but not always remains uncleared when I restart

Matthew Cronin

Sounds like a plan. Tell you what when it happens next also try resetting one of your trip computer counters and see if you also see a mileage pattern. It could be adaptive depending how you drive or it could be close to clockwork.
Matt