S205 start/stop not working

[T80ltn]

Hi all,
I have a C220d sport S205, had it for approx 5 months and the start/stop has never worked and recently an error message "start engine, see owners manual" keep popping up, the car starts ok every time and doesn't sound like its struggling to turn over but the other day I was getting the message coming up and I had the boot open for a while, probably about 15 minutes, and when I came to close it, it was dead so I started the engine and hey presto, the boot closed ok. I can only think this is a battery problem but looking a bit further into it not sure whether it would be the main battery, the auxiliary power supply or anything in between, last time I checked the battery with the OBD reader, which was not long after I had the car, it was ok.

 

[wongl]

How old is your car? Is the OBD reader showing any error codes?

 

[markjay]

As you pointed-out, the most likely cause is one or both batteries. I would start with replacing the main battery (although the chances are 50-50), but as wongle said, check for fault codes first.

 

[T80ltn]

Hi, the car is 5 years old, (2015), no fault codes showing now, although did get a fault code saying the nox sensor was goosed and had that replaced but no other fault codes showing even on completion of the sensor job, also, when I did check, the voltage of the battery was about 12.5 volts standing and about 14.5 when running.

 

[T80ltn]

Also, I dont have a clue where the auxiliary battery, (or capacitor as I've been told it is), is located, and is changing both batteries pretty much a diy task? or is it something that will need to be done by an authorised repair shop?

 

[GeeJayW]

Also, I dont have a clue where the auxiliary battery, (or capacitor as I've been told it is), is located, and is changing both batteries pretty much a diy task? or is it something that will need to be done by an authorised repair shop?

I think the auxiliary battery (a capacitor) is somewhere in the passenger footwell. Ours was changed under warranty, so I don't know exactly where it is. It's a common failure, my mate's failed too.

 

[wongl]

Also, I dont have a clue where the auxiliary battery, (or capacitor as I've been told it is), is located, and is changing both batteries pretty much a diy task? or is it something that will need to be done by an authorised repair shop?

Are you able to put your main battery on charge via a battery charger? It may be that your main battery is low and need an overnight charge to get it back up to full capacity. This is worth a try before you go round replacing the battery.

If you have a capacitor as the Aux Battery, then this should not need replacing unless you get a warning message about the Aux Battery being faulty or requires replacing.

 

[T80ltn]

Are you able to put your main battery on charge via a battery charger? It may be that your main battery is low and need an overnight charge to get it back up to full capacity. This is worth a try before you go round replacing the battery.

If you have a capacitor as the Aux Battery, then this should not need replacing unless you get a warning message about the Aux Battery being faulty or requires replacing.

I'll give it a good charge 1st and also see what the OBD says after, thanks for all the advise, I'll update later