Stop-start system

I have 2015 Mercedes-benz E220 Type 207 diesel coupé which has done about 61,000 miles. The engine number is 65191133038361. In Economy mode the stop-start system has always worked very well, but recently this has changed so that it may only function after an hour or more going reasonably fast. After a recent long run, it seemed back to normal, but now it’s again only cutting in after a long time. When it does function, it soon ceases to do so.

I understand that the battery life of a car with stop-start is typically about four years, and this car is just over the four-year mark. Is there any cause other than battery decline which is likely to be causing this?

If a test shows that a new battery is required, can the change be done easily by keeping a slave battery on the jump-start points to keep all the settings, or does the new battery need to be coded somehow to the vehicle? John Foxon You have highlighted the most likely cause of the stop-start system operation occurring only after a longer run. This is when the battery has also had the best charge and will be in its optimum condition.

Your Mercedes is possibly also fitted with an auxiliary battery and, depending on the version, it is often recommended to replace both at the same time. I would also add from my own experience that although the batteries are not cheap, the main dealer is normally very competitive on price and this also ensures you have the exact specification battery.

The battery may be fitted with a battery monitor attached directly to the terminal but according to Autodata this does not need any reprogramming. The only cautionary note is that when the main battery is disconnected an LED test lamp should be placed between the + and – terminals on the leads to test for any faults in the onboard systems. If the light illuminates the auxiliary battery should be disconnected before replacing the main battery.

When fitting the new battery, no special operations are needed.