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Misterious battery drain

2K views 5 replies 4 participants last post by  kanundrum 
#1 ·
This is about a friend's 9-5 M2011:

there is a huge battery drain when the car is parked for an extended period of time (like overnight), regardless of if the car alarm is on or off. If the battery is freshly charged, current leakage is next to zero. But several hours later, leakage current springs up to about 6.5 A, several systems turn on: main engine relay, chassis control system, rear differential control module -- and stay on until full discharge of the battery.

Any ideas what's going on?

The info about what happens is from a local mechanic (a very experienced and knowledgable in older models, but not the new 9-5), translation is mine and can be not quite correct.
 
#2 ·
My best bet is the alternator is faulty, or not connected properly, after all it's what should be charging the battery while you run it, it may only be able to work while driving, but not feeding power back into the battery to charge up.

check the voltages before and after (when running) with a multi-meter, be careful though...
 
#4 ·
These cars have a pattern of failure with Batteries and Cables.

I had a car with this problem that tested good UNTIL I completely removed it from the car. The Battery was disconnected from the Car, left on trickle charge overnight and tested. Only then did it fail testing. Left in-car, it would always pass (and I have a High-Buck Tester...).

He needed a Cable too but that didn't resolve what he brought the Car in for. When it was all said and done I had to re-seat his TWICE Unit before half the Car's Systems would come back on-line.

-gp
 
#5 ·
Thanks for trying to help guys, I appreciate that.

Turns out, this is a known issue -- the bus, or one or more of the systems "stay awake", and unfortunately there is a whole bunch of possible causes for that, starting with parking brake switch or button on the automatic gear shift lever getting stuck -- to water getting into connectors in the rear wheel house and damaging them -- to God knows what else. They are still searching... I'll post here when (and if) they manage to fix it.
 
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