Can anyone please help!!!!!!!!!

I have a Mercedes 2001 C240 auto with Command. My problems started a few months back when the car wouldn't start. After calling out the RAC and replacing the battery as suggested everything seemed fine until four weeks ago. In the morning the car wouldn't start again, battery totally dead.
Sent car to a MBZ garage (who have been very helpfull) and was informed the command unit is draining the battery overnight (quoted £2k to replace). Since then have been using the car with the fuse removed for the command unit everything seemed fine, until last week tried the car in the morning and again battery totally dead.Now SRS light is on which i believe is a result of battery draining.
Can anyone please advise on possible cause or repair of command unit.

Thanking any help................

 

Hi,

I don't understand.
You state that the battery has gone flat despite the fact that the Command fuse has been removed.

I don't suppose you have started leaving the keys in the car have you?

Need to firstly determine that you charging system is OK. You should have 14.5volts with engine running circa 2000 rpm.

Next is the battery. How old is the battery? They last approx 3 to 4 years dependent upon Quality / spec.
Once below 12.5 volts the battery is irreverseably damaged.
A recharge doesn't reverse the damage although it might appear to give a new lease of life for a week or two.

The key to this problem is quiescent battery drain as the dealer has advised.
Need to measure what the drain is and determine what is causing the excess drain.

Usually caused by the body ECU is not going into deep sleep.
Often linked to vehicle thinking the key is in the vicinity in which case it doesn't go to sleep.

Stuart

 

Hi

Thankyou for your reply. The battery was replaced a couple of weeks ago. I was told by a MBZ specialist the command unit waspulling 1.5amps off the battery when keys removed. When the command fuse was removed there was no longer a drain on the battery. Which appeared to cure the problem, untilthe other day the battery was totally flat in the morning and the command fuse has not been fitted since being in the garage. I've checked the voltage when engine running and is ok 14v. The keys are always in the house. Would be most grateful if you have any ideas.

Regards

Mike

 

Quiescent drain should be milli amps.
1.5 amps is more like the normal Command power consumption.
If indeed the drain sis 1.5 amps something is wrong.

However:

The body ECU goes to sleep in stages.
It does not go to sleep as soon as you turn the ignition off / remove the key.
It takes approx 5 to 10 minutes and certain conditions have to be met.
i.e. If key is in the car it doesn't go into full sleep.

I do not know the full set of conditions.

So my question is how did the dealer measure the quiescent drain?

If a door was open / opened it wakes the system up so the Command current may well have been 1.5 amps. Likewise if the hood / trunk are opened.
Only way to measure quiescent current is to remove +ve battery terminal and reconnect in series with you monitoring equipment (multimeter or whatever) and run the leads outside of the vehicle .
Take care that when shutting the door on the cabling you don't create a short.
Generate a current drawn vs time graph.
Starting from the moment you shut/lock the door with everthing OFF.
Do this initially with the Command disconnected and then with it reconnected (fuse back in).

You may find that the Command is in fact not the problem. Maybe there isn't a problem any longer and the problem was actually your "about to die" battery.

Quiescent drain after say 10 mins should be approx 50 milliamps. I don't have the exact MB figure for this.

Stuart

 

Hi stuart,

Firstly want to say thankyou for taking the time in answering my question. The MBZ Tech is not in work until Monday, i going to try and find out how he measured the current drain. Will keep you informed if ok.

Regards

Mike