LoFox

Hi Guys,

I've done some reading and searching on the forum and it seems that other users have been having issues similar to mine, but not quite the same. On my 2010 C63 I have no problem starting the engine but at times (so far 2 times in the past month) I've had the car completely die when I press the START/STOP button to turn off the car after driving

Generally the car will go through its normal shutdown process, lights turn off, radio stays on and when I open the door the radio shuts down and retracts back into its compartment. (Everyone is probably familiar with this.)

Now the problem, at times when I press the START/STOP button the motor turns off and all electronics die, the radio stays up but the screen is off, when I open the door the steering wheel does not lift, etc. Once outside the door cannot be locked or unlocked using the remote, nor do ANY buttons inside the car work ... the car is 100% dead.

Naturally, I think that the issue is cased by the battery, and as soon as I jump it all electronics come back to life and the car completes the shutdown process. The one thing that I'm not sure about is if the battery is actually bad or if there is something wrong with the alternator (or other component responsible for charging the battery.) I had the battery tested at a local parts store and they claim that it's fine, but since the battery is ~4-5 years old I'm not sure how much I believe that.

Your opinion on this issue would be greatly appreciated.

jcfay

I'm sure others will have a better answer for you, but at that age and with what you're describing it sounds like a battery as you suspected. Pop a new one in and see if that fixes it. Doubt your alternator is bad based on your description, but think you may be right about batt.

LoFox

Yeah my thought exactly, I ended up removing the batt, charging it to full and then testing it ~15 min after it has been 'charged' it it was down to ~70%. I picked up a new battery, but I should have paid closer attention because I'm pretty sure MB uses glass mat batteries and I've replaced it with a standard lead acid The replacement battery is listed as being compatible, but I'm not sure if a switch from AGM to lead-acid will cause charging issues, generally you need to reprogram the ECU to let it know that a switch was made.

Currently the car starts just fine and the new battery is holding a charge, no bizarre MILs have popped up which is usually a sign of charging issues in this case so I'll do some more reading and see how the car behaves over the next week.

-Marlin-

When you removed the old battery, did you keep power to the ecu? Or did you just pull the leads off and put the leads back on the new battery?

Reason I ask is that I may need a new battery in the upcoming months and I have read that it is a good idea to maintain voltage while replacing the battery so as not to allow the ECU to go dead.

LoFox

I did not, I had the battery disconnected and car with zero power for ~2 hours, which I think might be the reason why I got a temporary code thrown that triggered the MIL. I'm not sure if the same thing would happen to you, but the code is potentially from a random module (which ever one happens to throw it first) but related to a Read/Write problem for the overall system (since the various ECUs have no power)

I've been doing some online reading on maintaining ECU power while swapping the battery so I definitely recommend that you do the same. From what I've read so far it seems that all sources agree on keeping power to the ECU during the swap. (Most of the info came from BMW forums.) Overall pulling the battery and leaving the car with no power doesn't seem to have any lasting effects as the MIL went away ~4-5 hours later after doing some driving (nor were there any noticeable performance differences while the MIL was on)

Please share any info you find on this thread, I'm sure other users have similar questions.

SCD-1983

I'm interested in this issue as well, disconnecting the battery for a short period of time should be possible. I want to work on my steering while soon and I need to disconnect the battery due to the airbag deployment risk.

Thanks everybody for the great answers.

-Marlin-

FWIW ...


I really like his videos. Here he is going over the process he follows for MB battery replacement.

LoFox

Nice! Very good set of videos. (He does goes a bit overboard with his ominous warning of unplugging the battery, which might scare off some people .. but very good points.)

I think some earlier pre W204 models (or pre 2009 in general) have had issues with total voltage loss which might result in several fault codes and the need to reset one-touch open/close power windows ECU, sunroof ECU etc. I think that many ECUs in models from 2010 and higher are better with maintaining memory during a total power loss, most likely due to better onboard flash. (As a note, usually if you pull the positive terminal the EFI ECU will lose any 'learned' fueling setting such as fuel trims, also ODB2 readiness codes and potential pre-stored MIL fault codes.)

For the user looking to do work on the steering wheel you might need to also disconnect any secondary battery if you car is equipped with it (a little bit of info here: http://www4.mercedes-benz.com/manual...63e12239.shtml but be sure to do additional research on any ramification of disconnecting all batteries and if it's even necessary for your model.) In general, I would recommend looking into disconnecting the terminal for the airbag too and seeing if that is a better approach.

As a note, for electronic safety please be sure to disconnect the positive(+) terminal first and when reconnecting, reconnect the negative(-) first followed by (+) terminal.