My a207 just didn't start when I got up in the morning, no crank, headlights don't work, horn doesn't work and wipers don't work, but all other electrics do, don't have much knowledge on electrics, any help appreciate

 

Sorry to hear of your troubles. Rebuilding and engine from a bare block would give me far more joy than chasing electrical bs, which I've had a bit of.

I'm unsure what year your cabrio is or optiors fitted, but I assume all 207's have the "smart charging" system. Long story short, our alternators do not just pump out 14.X volts to the battery while running. There are conditions to be met, etc. To spare you reading a novel here, look into getting a surface level understanding of that system.

Needless to say, you of course need to confirm the state of your batteries (you may or may not have aux battery), alternator, and starter. The aux battery doesn't affect startup, but I'm just throwing the generals out there. Starters are in the top 3 biggest draws on our electrical system.

I go back to the smart charging system again because it often keeps our batteries at a very low state of charge for extended periods, often completcompletely unknown to you/us until something prompts you/us to have a look. I was having my battery drain down to 11.9 or 11.8 from full charge in about a wk. I did a parasitic drain test via an old Humble Mechanic youtube vid and saw my instrument cluster was a subtle possibility, but not enough to warrant concern (yet). The alternator's behavior and amp draw is visible through our instrument cluster, which I watch while driving but can sometimes display .05 volts less than "reality" due to loss from signal transfer through CAN Bus, etc if I understand correctly.

Lastly, I did a thorough inspection of all chassis grounds that I know of (11 or so? Along with at least one under front carpet I did not inspect), and I cleaned them all. Cleaning them has had my charging system hold full charge for over a month (opposed to a wk) and smart charging is constantly pumping out 14v when it detects the battery needs it. These issues are difficult to say the least. Get codes read, see what the modules in the car have to tell you, get your charging system checked as well as associated fuses and relays and take it from there. I hope this is of some help.

 

Thanks for a reply, it's 2013, it has a battery under the bonnet and a small one in the boot, checked fuses all fine had a code reader on and it couldn't read anything, got another mate coming with a better reader tomorrow to see if I can get any codes

 

if it were me i would use my multimeter to check the voltage on the battery. Should be around 12v.

If voltage looks fine i would check the fuses, like you say you have.

With the key in the ignition turn the car on. Can you shift P-R-N-D ?

Try another key, just to rule the key out?

Use a Mercedes specific OBD scanner. A generic scanner will not be as detailed.

 

It's a manual, and main beam light is now lit on dash even without key in

 

"Main beam light lit on dash even without key",

As in, the dash indicator that main beams are illuminated? Are the main beams actually on, or does the dash just say so? Keyless go fitted? Your 1st post hinted at many functions that a bad main battery will kill off, yet an auxiliary battery will let live if I'm not mistaken. I only have a main battery in my pre facelift (2010) 207. I did think that main beams are powered by main battery though, while internals like radio may be aux battery? Again, I'm not 100% on that but just leading to reiterate what Tim said about at least getting a multimeter on the battery and seeing where it is.

Also as Tim said, an MB specific scan tool/ something capable of talking to all of the modules is critical (ECU, Front SAM, Rear SAM, Central Gateway, etc). Obviously there's more than just a dead battery that can create a no start condition and good voltage means little if cold cranking amps are not sufficient. Again, you mentioned a few other external functions not working so hopefully it is just a battery or something of the like.

And again reiterating Tim's post, a bad key will certainly leave you stranded yet provide some functions. I've been through that with a W203 C230 and dash did light up, internal functions worked and believe I had headlights, but no start.

 

> Short Term...
Use a smart float charger such as a CTEK from Amazon...

Your batteries may have been rendered useless by deep discharge to the point you may have a larger set of issues with [main + aux] being useless.

> Long Term...
You will need to find your source of "battery drain while parked" starting with a chassis scan report of faults.


> Holiday Gift Idea...
A little portable jump pack is great insurance and may pay for itself when you least expect it...

 

Thanks for reply, bought both new batterys today still no joy

 

"no joy..." as in no crank with a new battery???

Something's going on...
"Main GND STRAP" located all the way under chassis - Try an easy bypass between chassis GND and engine GND.

Of course as always scan the chassis for obvious clues

 

Yeah no crank, I'm not well up on cars and don't know what gnd is,?

 

GND is the common negative voltage shared by the chassis.

Also car may be ignoring your key or not finding it. Try to insert key into ignition slot.

 

I tried both keys, in ignition, I think something is draining my main battery, as the battery seems to be loosing charge after 2 days

 

No crank with new battery
and battery drain in about 2days.

There's a good chance both drain and crank issues are linked.

Now is a good time to scan the chassis for a complete fault report.

The other option is to through lucky arts at this blindly but it gets expensive with little results ...

 

2 friends have tried scanning with 2 different code readers and both said unable to read

 

You can try using an MB compatible LAUNCH Scanner such as Creader elite
and perhaps this explains why nothing's really working

Can you disconnect all power for 15mn then reconnect both batteries.
This will be an effective Reboot.

Perhaps something's shorting one of your CAN-Buses... such as a wet module

 

Before this happened both scanners worked on my car, and now you've said damp I did forget to put the plastic lid on the front Sam a couple of days prior to the problem and did have a couple of heavy rain falls, maybe it might have got damp, how would I dry it out, would spraying wd 40 on it get rid of and wetness??

 

Now you can start from the beginning with fuses and maybe looking for water or something near the Front SAM / Engine compartment Fuse Box,

 

I don't want to ruine your hopes but realistically:
Your Front SAM is done,
95% chance it's beyond repair...

It's built by Bosch without basic protection,
It's positively non reparable electronic.

 

Oh no, it's gonna be expensive if that's the case

 

Has all the necessary protection, but some times mechanics forgot to lock the cover

Anyway is so cheap as nobody care to repair it.

 

What's cheap

 

when its all said and done... you're looking at $1.5k

somebody needs to extract your SAM
Source a matching replacement
extract your SAM's coding
Program replacement unit
Install replacement unit
Test the newly installed SAM

Not a spark plug job!!

 

Till spending for a new SAM a proper diagnosis is the best approach.

 

Yeah, I'm going to get an auto electrician out, don't want to spend on something that might not fix it

 

The diagnostic is free with repairs - It will be simple.