Before you go to that expense check to see if you do have stop/start and regeneration, lift hood and remove plastic cover fixed to the starter battery(3 clips), if the negative battery clamp, the black lead has one of these in pic below you have stop/start and regeneration, if there is no small box attached to the clamp you don`t. If the battery is original, it may be the battery, My C-Class Coupe (same engine as R172) has original battery stamped Sept 2011, it`s still going strong but I am in the UK.
If you don`t like stop/start (for me it`s a useless piece of extra tech to go wrong) just disconnect the sensor arrowed in pic, this will deactivate stop/start, there will be NO CEL on dash and the car drives normally, (you do loose brake hold but that`s all), you get an extra bonus which is far more advantages, well it is for me. With the sensor disconnected the EMU which controls the alternator goes into a pre-arranged charging mode(as it does if sensor fails) and instead of only charging battery to 75% will now charge it to 100%, at between 13.8 volts float and 14.2/3 volts charge, link below.
, I just reread you post, I own 2 Merc`s a C-Class 2012 model and an SLK R172 2015, on the C Class the symbol stays yellow on dash when stop/start is not working, when stop/start is not working on the SLK there is NO
symbol on dash, same as your car.
#104 Old 3 Weeks Ago
I had a bit of time on my hands this evening so I have now implemented my switch idea. I had the switch already left over from another project and some 2 core cable of the appropriate size.
I routed the 2 core to the cabin from the battery compartment using the convenient grommet just behind the battery. The sensor wiring has a red power cable connected to the positive battery terminal and a blue one which is the sensor output to the rear SAM. I’ve put the switch in the blue signal line. I’ve installed the switch in the kick panel above the pedals, so it’s in reach from the driver’s seat but out of sight.
So now with the switch closed it’s OEM behaviour and with it open stop/start and brake hold are disabled but crucially cylinder deactivation is unaffected!