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Battery drain - Command CANbus expert help?

109K views 29 replies 13 participants last post by  cowboyt  
just by reading this it looks like you are getting to deep into diagnosis before starting with the basics. first things first are hooking a meter up to the battery and checking for an actual draw. you are checking the amperage draw of the battery. you hook the meter to the negative cable and then the other lead to the negative post. you should be seeing anywhere from 20ma-80ma depending on what options your car has. you need to see if you even have a draw before taking a guess as to whats wrong with the car. another thing is just cause the voltage reading is 14v doesnt mean the alternator is producing the full current to charge the battery. voltage and current are 2 seperate things. your alternator could be only putting out 50A which is not fully charging the battery. last thing is exactly how long before the battery goes dead??? you havent really said that the battery does go dead. i ask because alot of customers tend to leave a car parked for an extended period of time and thing that the car should just fire up with no issues.
 
when you do the draw test, all doors need to be locked and trunk locked, the car needs to be as it is when you are away from it, this gives you the most acurate readings. also 4 minutes is not long enough to wait, sometimes the car wont fully go to sleep for up to 20 minutes depending on what options the car has. now if after 1q0 minutes for saw you are at 450 miliamps start pulling fuses 1 by 1 untill the draw drops to 20-80 miliamps. then with that same fuse reinstalled the draw should go back up. draws arent at all hard to diagnosis as long as its happening at the present moment. what becomes an issue is when its intermittent and trying to catch it isnt easy. at the dealer we had what is called an sd scan tool on the das which hooks up the the can network and will monitor the car for extended periods of time and when a unit wakes up it detects it and stores the info. its better then sitting and watching the meter.
 
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