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I have a 97 M3 with a parasitic battery drain. I’ve checked…

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Hello I have a 97...
Hello I have a 97 M3 with a parasitic battery drain. I’ve checked all fuses and relays, wires for a short, removed the alternator and the starter and it is still pulling 4 amps! What could be causing this?
Submitted: 8 months ago.Category: BMW
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Answered in 7 minutes by:
11/13/2017
BMW Mechanic: peterpete190, Auto Technician replied 8 months ago
peterpete190
peterpete190, Auto Technician
Category: BMW
Satisfied Customers: 33,003
Experience: Over 17 years diagnosing and repairing vehicles.
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Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

How long did you wait in between pulling each fuse to observe the drain to see if it went down any?

Did you have fault codes checked/read out at all as well?

Let me know,thanks Pete

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Customer reply replied 8 months ago
I waited maybe 20 seconds. I don’t have the tool to read codes maybe I should buy one.
BMW Mechanic: peterpete190, Auto Technician replied 8 months ago

O.k.,what happens is when you pull a fuse it takes around 10 minutes in some cases for the computers to power down.20 seconds isnt enough.Here is the procedure I follow:

what needs done is to leave the key out of the vehicle with the windows rolled up and make sure everything is off with access to the battery.

Set the meter to amperage or milliamp and disconnect the negative cable from the battery.Put the leads in the multi meter the correct way (negative in negative and positive in the amperage or milliamp slot if equipped).

Connect one cable from the meter to the ground cable that was connected to the battery and the other lead to the ground terminal on the battery,this way the current is flowing through the multi meter.

After around 5 to 10 minutes see what the meter reads for a amperage draw.Normally you want to see less then 50 milliamp or less then .05 amp.

If you see over this amount of a battery draw/drain then your vehicle has an electrical component draining the battery.

From here you would remove one fuse at a time with the meter still in place and observe the reading on the meter until you come across one fuse that allows the draw to read below the 50 milliamp.This is the fuse or circuit that has the component on it that is drawing down the battery.Make sure when you remove one fuse if it is not the issue reinstall it and move to the next waiting a minute between each fuse removed to get an accurate reading.

Once you find the fuse or circuit its on then you would look on a wiring diagram to see what that fuse powers and unplug each of those components one at a time until you locate the component causing the draw then this component would need replaced.If you need help knowing what is on the fuses circuit once the fuse is located let me know.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

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