luthepa1

Hi Everyone,

Seeking some advice diagnosing my car problem. I could not start my car this morning as battery had lost charge. Everything powered on OK but just not enough cranking power. And I noticed last two days that when starting car it sounded like it struggled a tiny bit, like the battery wasn't fully charged. I should have taken that as my first sign.

So I did some tests using a multi-meter, a Bluetooth battery monitoring device (which is attached to the battery directly and has been for the last year) which I connect to using app on my phone and finally the Battery Info menu in the secret engineering menu. NOTE: all voltage readings between the multi-meter, Bluetooth device and cars engineering menu are aligned and read the same.

1) So using multimeter and my bluetooth device, my battery reads 12.3v with car off.
2) Start the car and the voltage sits between 14.2v to 14.6v. Ok, thats good.
3) Put the car in drive and go for a 7min drive on the road and suddenly the voltage drops to 12.x volts. Ok that doesn't not seem good at all.
4) get back home, put the car into Park, and suddenly the voltage goes up to 14.x volts again.
5) put the car back into Drive but stay stationary, and suddenly the voltage drops to 12.x volts again.
6) putting car back into Park again but voltage stays low at 12.x volts. I turn car off and quit for the day.

Car: 2010 C63 AMG M156
Battery Specs: CCA850 RC160 95Ah
Car Mileage: 130,000 Kms
BT Battery Monitor Device: Powertech Battery Monitor

Alternator visually looks very clean to my surprise but to my knowledge I dont believe its been replaced.

Attached pics charting out voltage levels.

* So does this issue seem like Alternator
* or maybe even just the voltage regulator (at 130K its probably well and truly worn down)
* or does this seem more serious than alternator/voltage reg?


Appreciate any feedback and advice.

Paul.

luthepa1

So while taking my boy to school this morning I continued monitoring and noticed something interesting that makes me question if kind of software/electronic logic is malfunctioning. So battery fully charged overnight and is at 12.7v car switched off. Start car and voltage in the 14v range. Put the car in Drive and start moving and you can see the voltage slowly decrease to 12.5v +/- 0.2v of 5 second period. The whole time I'm driving the voltage always in the 12.x range even when stationary. When I get home, park the car, and put it into Park, the voltage still in the 12.x range UNTIL I open the drivers door, with the car still running, it suddenly ramps up to 14.x volts again!

So it feels like some sort of car logic that dictates voltage regulation is not playing ball. I know when you switch the car off, its not really off until you open the drivers door. Then the car is off so not draining the battery.

I understanding some people might see my post and think its very similar to so many other posts on the forum here and use the search but I'm not finding anything like my situation where it seems like logic misbehaving. However what I think of as some kind of logic might just be coincidence and in fact is a dodgy voltage regulator. Please any advice much appreciated.

Mort

Do you have Option Code 909 Alternator Management. I believe it has something to do with the small black electric box with the wires going to it on the negative terminal on the battery. It has been mentioned on here a few times. That is all I know about it personally but someone else may be able to help you out. Batteries do go bad and if they discharge to a low level can be permanently damaged.

luthepa1

Cheers for feedback! and yes! Earlier this morning just after my 2nd post I tried disconnecting the battery management sensor and now I am getting 14v charging. Sweet!

So now I will source a new sensor. I don't want to leave it unplugged as after researching it does inform the ECU about a number of things or put it another way, it does provide decision making for an number of code functions in the ECU.

Mort

Sounds good, lets hope a new sensor does it.

luthepa1

Actually I just got to thinking and now researching, is there a battery management system reset procedure? I had my battery replaced about 12 months ago and so I am thinking that my current sensor may not be faulty but rather needs a reset. Is there something that needs to be done on the car to indicate to the system that the battery has been replaced?

BLKROKT

Likely dead battery if unplugging the IBS sensor worked. Temporary solution, just causes the alt to put out 14V all the time instead of varying it. It sounds like your battery isn’t holding a charge.

Also, if you’re at 130k miles you are likely in need of a new voltage regulator. They’re usually good for ~100k miles.

IBS doesn’t have a reset or calibration function like BMWs. Nothing to do there.

luthepa1

A dead battery could cause the weird behavior where the charge voltage is at 14v until I put it into drive where it drops to 12v?

oskichohfi

Hi, I have the same problem as yours.
did you get any solution?

roadkillrob

Looking at his symptoms and how low his battery voltage went when cranking, I would guess buying a new battery fixed it.

How old is your battery?

oskichohfi

Already replaced the battery and alternator. But the problem remains
When you start the car it is normal, 14.5v ib 10-30
When start the trip goes to 12.5v ib -5 - 0
If I shift into reverse, it goes back to 14v with positive ib
When it goes back to N or D it drops to 12.5v
If I open the door it goes back up to 14.5v.
What can it be? Sounds like a communication error to me.

catmandoob

I just kind of went through this as well. In the end it seems this is normal operating for our charging systems. After much digging and a good bit of help from great folks here on MBWorld don't lose your mind over it. If you're battery isn't charging you will know by going below 11v or 10v as resting stage. I replaced my alternator(was going to do regulator but chased this down as you are) and battery and everything has been fine, I probably just needed a battery in the end and alternator probably has a good few thousand more miles left.

Anyway, moral for the story is yes, the C63 has a charging system that is constantly varying the voltage. Here's a link to my own thread https://mbworld.org/forums/c63-amg-w...ml#post8576366

Many of us have lost our mind looking haha, the whole point of the sensor is so the alt isn't tossing out full voltage all the time when it's not needed. That's the general principle at least.