ovehe

Hi,

Over the last two years, i've been experiencing periodical battery drain. Overnight the car won't start. At first, i replaced the battery, still had the same problem. A fully charged battery can be drained, to the point that the car doesnt crank, in about 12-18 hours. The problem is more evident during winter time (I live in Norway, cold winters etc), but it may very well happen all year, only that i need more amps for a cold (sub-zero celcius) start.

From forum searches i tried disconnecting both seats, but that can be ruled out. I handed the car into the MB dealer, but they couldnt reproduce the drain (5 days connected to an ampere meter). Of course - two days later, the battery was dead.

Few days ago, i entered the car to get something, noticed the fan from the overhead console was running even after all systems had shut down. Pretended to "leave the car" by opening, closing and locking the door. The fan continued to run for over 10 minutes. If i were at home, i'd connect my ammeter inline the battery pole/battery connector to measure the drain.

I've read about failing overhead console panels causing battery drains, so i of course put this one down on my list as a prime suspect. Problem is - ever since that, i cant reproduce the problem, and i cant really find much from internet searches except from a few people claiming that overhead console/dome lights/sunroof have been known to cause parasitic drains.

Do anyone have experience in symptoms caused when these fails, or any good tips on how to reproduce the error?

Could it also be that the overhead is just being kept alive from some other "electrical noise" on the canbus system or what ever (im no electrician), or is it most likely to be the other way around?

Any thoughts are very much appreciated.

Thanks,
Ove

acr2001

It could be the overhead panel, but you're right, if something else is keeping the CANBUS active then that air sampling fan may be running as a result. For example, on my 05, if you press the rheostat on the gauge cluster to turn the cluster on (after the car has gone into sleep mode) the CANBUS goes active and air sampling fan comes on, COMAND even does it's pre-boot and spins up the nav DVD. But after about 20 seconds the cluster turns off putting the bus (and everything on it) back to sleep.

I suggest you disconnect the overhead panel and wait to see if it solves the problem.

Otherwise it should be possible with star diagnostics to determine which item is keeping the bus active.