Downhill -revving engine alarmed at noise

[Marc o Polo]

I wonder if anyone can advise re. the following, please? I’ve noticed that engine revs increase quite audibly when MP is going downhill and wonder if that’s normal for an automatic vehicle (40+ years a driver, but no previous familiarity with automatics until I got the MP!). If it’s a normal phenomenon that’s fine; but if not I’d like to know the cause – in particular if it’s something I’m doing (or not). Most grateful for any suggestions – thanks!

 

[Grand Tourismo]

I wonder if anyone can advise re. the following, please? I’ve noticed that engine revs increase quite audibly when MP is going downhill and wonder if that’s normal for an automatic vehicle (40+ years a driver, but no previous familiarity with automatics until I got the MP!). If it’s a normal phenomenon that’s fine; but if not I’d like to know the cause – in particular if it’s something I’m doing (or not). Most grateful for any suggestions – thanks!

What drive setting do you have selected ? E, C or S?
Also what rough type of hill (are we talking a Lake District 25% or more modest Cotswolds 10%)

 

[Marc o Polo]

Thanks GT, This just bugs me but it might be doing what's expected, so thanks for your time.. The setting is C: the very high revs only occur on Yorkshire drops - the type where there is a blind summit, then steep lengthy, descent. When in manual you would change to low gear to aid braking. All I do in now is control car with brake only???

Visited coast - Ravenscar, Whitby - yesterday and came across "slopes" and all was fine...... just a bit apprehensive if it happens again with traffic behind, on those real steep ones, having to bring down very high engine revs (and noise) by braking when the car is already going slow...

Not sure how to replicate so can't describe exactly what I'm doing wrong to cause this - I'm convinced at this stage it is down to me (and ignorance) and not the car...

Feel free - let's hear it, I'm braced for the embarrassment...

 

[Grand Tourismo]

Thanks GT, This just bugs me but it might be doing what's expected, so thanks for your time.. The setting is C: the very high revs only occur on Yorkshire drops - the type where there is a blind summit, then steep lengthy, descent. When in manual you would change to low gear to aid braking. All I do in now is control car with brake only???

Visited coast - Ravenscar, Whitby - yesterday and came across "slopes" and all was fine...... just a bit apprehensive if it happens again with traffic behind, on those real steep ones, having to bring down very high engine revs (and noise) by braking when the car is already going slow...

Not sure how to replicate so can't describe exactly what I'm doing wrong to cause this - I'm convinced at this stage it is down to me (and ignorance) and not the car...

Feel free - let's hear it, I'm braced for the embarrassment...

No embarrassment from me...whatever it is we are all learning together.
I used my van in N Devon on some fairly steep (and twisty) drops of circa 20% and did not experience your symptoms. I have my van generally set in E mode.
The reason I asked about engine mode is that I would select C or even S if I wanted to hold the revs a little higher when climbing steep gradients and did not want to force an upshift and loose momentum.
You could try using E to see if it helps but either way I suspect the engine is assisting you in braking down the gradient. It does feel a little weird but in an auto vehicle all you have control of is the brake pedal.

The manual suggests you drop into the manual flappy paddle mode and use M1 or M2 (as enclosed) to relieve the stain on the brake system, especially when towing heavy loads.

I guess that the Speedtronic setting will just apply your footbrake for you if/when the speed builds up too much.

Not relevant but related: On a particularly long and steep descent I did mention to my wife that I missed an exhaust brake (which is something that used to be fitted in HGV's years ago, not sure if it is now) to assist the footbrake system as it felt like I was giving the system a little too much but they have not yet failed or felt spongy afterwards.

Interesting that the manual says its best not to stop after a particularly heavy session as cooling the brakes in moving air is preferable than stopping.

Edit: and regarding backing up the traffic around you...let 'em wait!! It's live and let live. Almost all of them would prefer you get down the hill safe and steady than the alternative!

 

[Marc o Polo]

Great support GT, much appreciated..

Unfortunately I don’t have eco on my model v220, but I understand perfectly and take on board the other points you make. I can see how useful it would be to move into manual mode (yuk) so I’m going to have to get to grips with that. The tip about keeping going to cool the braking system is useful, too. Thanks GT, I’m not at all technical so I do appreciate your input, along with SBD and Steves (all) and others, IOU.

 

[Samebutdifferent]

It may be worth taking your MP to a dealer mentioning the problem and getting them to check it over.

From MB:
The heart of all Mercedes-Benz automatic transmissions is a high-performance micro-processor, which is designed so the transmission shifts as the driver expects and wishes it to react. Continuous electronic networking with the engine and chassis management systems allows the transmission computer to adapt to a wide variety of driving situations, and even to the driver’s style.

By comparing road speed changes and load, or throttle opening, the transmission computer can instantly discern uphill and downhill grades, and adjust shifting as a result. It delays upshifts on descents (for engine braking), as a driver is likely to do with a manual transmission. The micro-processor even considers cruise control and engine temperature in the shifting decision.

The computer also measures how fast the driver presses and releases the accelerator pedal. If the pedal is pressed relatively quickly, the transmission is more likely to downshift, for instance during sporty, more spirited driving, while upshifts are less likely when the pedal is released quickly. With normal pedal operation, shifts occur according to a basic program aimed at getting the best fuel mileage.

Sounds from the last paragraph that it learns and adjusts by how it is driven, maybe Lewis Hamilton was a previous owner It does seem that you are experiencing quite aggressive engine braking on steep descents.

I haven't had my MP long but have over the past few years experienced driving my wifes C class and a VW Transporter with a DSG gearbox, all have changed down when braking on descents to effect engine braking, it's been noticeable but not aggressive.

 

[Grand Tourismo]

Thanks GT, I’m not at all technical so I do appreciate your input, along with SBD and Steves (all) and others, IOU.

No problem at all... after all "team work makes the dream work!"
(more cheese than Cathedral City me)

 

[Marc o Polo]

It may be worth taking your MP to a dealer mentioning the problem and getting them to check it over.

From MB:
The heart of all Mercedes-Benz automatic transmissions is a high-performance micro-processor, which is designed so the transmission shifts as the driver expects and wishes it to react. Continuous electronic networking with the engine and chassis management systems allows the transmission computer to adapt to a wide variety of driving situations, and even to the driver’s style.

By comparing road speed changes and load, or throttle opening, the transmission computer can instantly discern uphill and downhill grades, and adjust shifting as a result. It delays upshifts on descents (for engine braking), as a driver is likely to do with a manual transmission. The micro-processor even considers cruise control and engine temperature in the shifting decision.

The computer also measures how fast the driver presses and releases the accelerator pedal. If the pedal is pressed relatively quickly, the transmission is more likely to downshift, for instance during sporty, more spirited driving, while upshifts are less likely when the pedal is released quickly. With normal pedal operation, shifts occur according to a basic program aimed at getting the best fuel mileage.

Sounds from the last paragraph that it learns and adjusts by how it is driven, maybe Lewis Hamilton was a previous owner It does seem that you are experiencing quite aggressive engine braking on steep descents.

I haven't had my MP long but have over the past few years experienced driving my wifes C class and a VW Transporter with a DSG gearbox, all have changed down when braking on descents to effect engine braking, it's been noticeable but not aggressive.

Thanks for pointing me to this. I reckon in the circs my best policy should be to monitor what happens for a while and see what happens - could be that things settle down as and when the MP and I get used to each other! Watch this space......

 

[Vandolfthegrey]

I've reported a similar issue, when braking to a stand from motorway speed, I had a very aggressive thud/bang when changing 2nd-1st. Happened twice on the same trip but never happened before or since. Van was hot and fully loaded. My dealer is aware and going to have a look at my next visit. Keep us posted if you find anything out please.

 

[pumpsmynads]

I've reported a similar issue, when braking to a stand from motorway speed, I had a very aggressive thud/bang when changing 2nd-1st. Happened twice on the same trip but never happened before or since. Van was hot and fully loaded. My dealer is aware and going to have a look at my next visit. Keep us posted if you find anything out please.

I’m going to take mine into the dealers tomorrow if I’ve time. When slowing and getting to about 15mph it drops from 3rd to 2nd (I thought it was 2nd to 1st but used manual to check the revs when it happens to work out that it’s 3rd to 2nd) and doesn’t seem to use any clutch (or whatever an auto uses) and the whole van judders and engine braking slows the vehicle. It’s very pronounced and not at all comfortable.

 

[Marc o Polo]

PumpsMNs I'd be interested to know how you get on.


Will do Vandolfthegrey.

 

[Vandolfthegrey]

I’m going to take mine into the dealers tomorrow if I’ve time. When slowing and getting to about 15mph it drops from 3rd to 2nd (I thought it was 2nd to 1st but used manual to check the revs when it happens to work out that it’s 3rd to 2nd) and doesn’t seem to use any clutch (or whatever an auto uses) and the whole van judders and engine braking slows the vehicle. It’s very pronounced and not at all comfortable.

Oh dear, keep us posted

 

[pumpsmynads]

Oh dear, keep us posted

Apologies for the lack of an update.
Van went in and I got a call at the end of the day saying that it’s likely goosed but that they have a call with Germany to investigate further in the morning.
Anyway, after speaking to Germany and linking the van to their computer, uploading various data, downloading various patches, flashing eproms was a phrase used too, it now all works fine.
I’ll keep an eye on it but it’s now perfect.

 

[Grand Tourismo]

Apologies for the lack of an update.
Van went in and I got a call at the end of the day saying that it’s likely goosed but that they have a call with Germany to investigate further in the morning.
Anyway, after speaking to Germany and linking the van to their computer, uploading various data, downloading various patches, flashing eproms was a phrase used too, it now all works fine.
I’ll keep an eye on it but it’s now perfect.

Woah, major engine remap/update...thanks for keeping us informed

 

[DPS20K]

I also had this very severe downshifting on my 2021 MP a couple of days after I picked it up at beginning of July. I booked into the local dealer and they said there was a transmission software update available for my vehicle so they installed it. It’s been perfect ever since. Wonder why a car straight from the factory needs a software update but it solved the issue.

 

[The fat controller]

Good to hear people's perspectives on this.

We've just got back from putting the first 1000 miles on the MP round Wales and that severe down change was pronounced and unpleasant. Especially as it seems worst under moderate braking so often was when meeting traffic on narrow lanes and moving towards the side of the road.... More than once my wife thought I'd hit something!

It did also seem to high rev on descents from time to time but I'm another with very little experience of autos so wasn't sure if this is in fact a good thing - vehicle utilising engine braking to assist?

I'll give the local MB a call and see if they will do a software update when I'm able... We'll be away again next week so it will have to wait a while unfortunately. Although I must admit I'm slightly disappointed that a new vehicle isn't updated prior to delivery.

 

[Method7]

You do have to question what kind of pre-delivery checks are made on new vehicles.. presumably the engine and transmission components used in the MP are shared across the MB range and I guess these components have control modules that come with pre-installed software [for what model] .. it makes sense that this might need checking and flashing to ensure it has the correct (current) mapping for the vehicle it has been applied to.

I bet there are loads of vehicles out there running incorrect software versions. It’s really scary considering some of those vehicles have auto-pilot and other variations of intelligent cruise control or driver assist functions.

I would presume the correct mappings on the 300 would perform in a way similar to any other MP where gear changes are hardly noticeable in either direction, up or down. On a steep down hill the car is happy to run away just like a manual would, this is controlled as you would in a manual either by using the brake or opting to do a manual override on the gearbox and selecting a low ratio and use engine breaking that way.

Ordinarily there is very little engine breaking on the MP, I guess this is part of the economic setup, the car tends to just coast along when you lift off the throttle. When cruise control or speed limiter is selected that is a different matter, the car will then prevent excessive speeds but that seems to be managed by applying the brakes, you can feel it in the pedal and the bite point changes - this can be a bit of a surprise if you need to apply the brakes at the same time since there is no free pedal and a gentle touch can result in a very sharp decrease in speed.

 

[Webbah]

I just picked up my 2021 300d MP 4Matic yesterday and experienced the severe thunk/jolt when downshifting from 2nd to 1st as well. Brought it to service today and they said it is a known issue and are applying the software remap update. Told me it should only be about 30 minutes. Also I mentioned the MBAC was on Generation 1 and not Generation 2. He said this is also a software update and will try and do that one as well today even though I just came by without an appointment. Fingers crossed!

 

[Marc o Polo]

How did you get on Webbah? Really interested to know..

 

[Webbah]

How did you get on Webbah? Really interested to know..

All fixed! Very pleased. The MP now shifts normally and the MBAC was updated as well. In order to make sure you are syncing with the correct MBAC app settings I had to delete the app completely, then remove the Bluetooth connection from both the MP and the iPhone. Then reinstall and the app will prompt for the pairing using Gen 2 profile. After that I could see all the extra settings for heating, and the ability to extend and retract the Pop top roof.