SLK55 eco not working!

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Not sure why anyone would want it working.
Because if it not working the 4 cylinder deactivation will not work , why would I want to drive 200 miles on the motorway at 70 - 75 mph and get less than 30 mpg when I can get 33 with virtually no difference in driving experience! I can switch it off by simply putting the gearbox into Sport mode
 
** cough **

Do you know if there are many or any resets to do when the main battery is replaced in these cars, radio codes etc?

Also, does the new battery have to be coded to the car in any way?

Thanks again.
 
I have no idea.

I would expect that windows, sunroof etc may need reset. Your handbook will explain how to do that.
 
Do you know if there are many or any resets to do when the main battery is replaced in these cars, radio codes etc?

Also, does the new battery have to be coded to the car in any way?

Thanks again.
You have to reset the windows, which is in your manual.
Start the car with the doors closed and drop the windows.
Close the windows and hold up the door switch for an extra two seconds when they reach the top.
Obviously you'll know to input the radio code and adjust the clock, and no, the battery doesn't need to be coded to the car.
 
Hello

I thought I’d post an update on this for anyone who may be interested.

Both batteries were replaced and this made no difference. The fault appears to have been traced to a faulty brake pressure sensor. This does make sense as the stop / start works with the brakes. The sensor was not causing any warning light or causing a fault to be stored, but changing it appears to have done the trick.

Thank to people who replied to my questions.
 
The SLK55s do seem to have some strange electrical habits. Ours started doing exactly as you described in terms of non-functioning ECO mode (used only by the other half!!). I originally put it down to her 3 miles round trip to the shops and lack of decent runs - this was compounded by the lockdown with little other use.

Out of the blue the near side door refused to open! Despite all attempts to release it, it firmly refused to budge for two weeks, and then - voila, it opened again! It continued to work for another two weeks and then back to 'lockdown' - literally.

A trip to Sandown revealed that the door module had failed and needed to be replaced - the only available one being in a dealer warehouse in Ireland (non in Mercedes UK or Germany!!)

Replacement part fitted 4 weeks ago and so far, no further door problems or ECO issues.

Neither battery replaced :)
 
Apparently the brake pressure sensor had to come from Germany so took some time to arrive.

We were also told that there were three outstanding updates for the car which were also installed.

My wife noticed a difference straight away with improved smoothness and response. It will be interesting to see if there is any improvement in economy after these updates. With the eco function not working, fuel consumption appears to have increased by about 20%. The stop / start isn’t used much usually, but the cylinder drop is. I’m a bit surprised that the difference wasn’t more. The car usually returns about 37 mpg on a long run with cylinder drop, it’s been closer to 30 constantly running as a V8. Just as a comparison, my 6.2 C63 pre facelift get about 26 to 27 on a long run.
 
@Oscar 473 - Thanks for closing this one out: I'll commit it to memory in case stop/start goes into a sulk on my wife’s SLK55 :)

Totally agree about the economy benefit of the cylinder shutoff on longer runs - it can make a big difference. I was surprised to find that it will happily drop down to 4-cyl running even at higher speeds: the limit seems to be around 110mph on the flat, after which aero drag is obviously too great and it reverts to all 8.
 
I expected the cylinder drop to be a bit of a gimmick until my wife got the car, but I’m surprised how often this cut in, even when the car is cold.
 
Oxygen sensor. My Eco stopped working on a 172 55. Replaced both batteries. Still didn't work. Diagnostics said oxygen sensor fault. Replaced that and now all good.
 

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