Parasitic draw

[Torched10]

Found thus very helpful

https://www-wikihow-com.cdn.ampproj...ww.wikihow.com/Find-a-Parasitic-Battery-Drain

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[WItoTX]

Yep. Pretty simple. Yet dealers get it wrong all the time.

 

[Mike Pfeifer]

Some of those methods may cause misinterpreted results. In older cars, they work fine, but modern cars can trip you up if you don’t understand the systems those fuses are for. Also, pulling fuses one at a time may cause the vehicle to “wake up” leading to frustration if noticed, and incorrect diagnosis if not. Sometimes disconnecting the battery will cause a vehicle to not power down correctly when the meter is connected in between and circuit re-established.

The way I currently do this type of diagnosis is to use an inductive amp clamp on the battery cables (either positive or negative depending) and check voltage drop across the fuses while they are still installed. This 100% works and is being taught in BMW factory training now as the only correct way. The measured voltage drop across the installed fuse, in mV, will have a direct relation to the current flowing through it and is repeatable every time. This way you identify the circuit while not disturbing the vehicle systems. I have a chart at work I can take a picture of and show. Moving the amp clamp around can help isolate specific areas of the vehicle by placing it on other “down-stream” positive leads, like the cable going to interior systems or to under hood systems. I like to think I’m pretty good at parasitic draw diagnosis, so feel free to ask questions, I’m sure my comments are going to raise a few lol!

 

[Mike Pfeifer]

Here is a good video showing the voltage drop across the fuse method: YouTube Video

 

[Jaymar]

Some of those methods may cause misinterpreted results. In older cars, they work fine, but modern cars can trip you up if you don’t understand the systems those fuses are for. Also, pulling fuses one at a time may cause the vehicle to “wake up” leading to frustration if noticed, and incorrect diagnosis if not. Sometimes disconnecting the battery will cause a vehicle to not power down correctly when the meter is connected in between and circuit re-established.

The way I currently do this type of diagnosis is to use an inductive amp clamp on the battery cables (either positive or negative depending) and check voltage drop across the fuses while they are still installed. This 100% works and is being taught in BMW factory training now as the only correct way. The measured voltage drop across the installed fuse, in mV, will have a direct relation to the current flowing through it and is repeatable every time. This way you identify the circuit while not disturbing the vehicle systems. I have a chart at work I can take a picture of and show. Moving the amp clamp around can help isolate specific areas of the vehicle by placing it on other “down-stream” positive leads, like the cable going to interior systems or to under hood systems. I like to think I’m pretty good at parasitic draw diagnosis, so feel free to ask questions, I’m sure my comments are going to raise a few lol!

All of this I'll second, as well as add watching the ammeter as the car goes to sleep. The draw on the battery will step down as the vehicle shuts down into it's sleep mode so watching how much and when the current drops can give you some insight into what each module is drawing. Only helps if you have a frame of reference for that particular vehicle mind you and you have to be patient and not touch anything.

 

[5doorsoffury]

fuse method works i have used it many times. the fuse method is really for identifing the module involved then from there further investigation can take place like a bad door trigger keeping a bcm from going to sleep ect. i would reccomend a quick dissconect battery clamp, (2) 12 awg test leads and a good ole meter. no clamp meter bullshit... theres no varying magnetic field for a clamp to pick up on with dc so inline current checking with standard meters only... like a fluke 77 ect..

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