Advanced BMW Parasitic Battery Draw Diagnostics

September 7, 2013 | Reply More

Whether you call them draws or drains, tracking them down isn’t as easy as it once was. These procedures and tools will help.

Forget about putting a digital multi-meter in series with the feed side cable as per the BMW TSB. The quick and easy way to is to put a sensitive and accurate amp clamp over the negative battery cable.

Forget about putting a digital multi-meter in series with the feed side cable as per the BMW TSB. The quick and easy way to is to put a sensitive and accurate amp clamp over the negative battery cable.

Diagnosing battery draws can be time consuming, especially when the draw is intermittent. We are going to discuss different methods of finding battery draws and the importance of using the right tools. The more strategies you have to attack a parasitic draw, the better.

Square one

The first step to diagnosing a battery draw issue is to always check the basics. Test the battery and the charging system. Any amount of A/C ripple more than a few dozen mV should raise an eyebrow, although theoretically speaking the vehicle should handle several hundred V AC without burning up. If you measure even a small amount of AC ripple, it shows that the diodes in the alternator are damaged, making it possible that they are drawing power when the engine is off.

Another basic step is to do a health check and see if there are any codes stored in modules that indicate an internal defect or communication issue. A battery drain problem can often be symptomatic of an issue that is setting DTCs in the vehicle.
Furthermore, when trying to discern whether or not you even really have a battery draw or just a really weak battery, expect to find a DTC. If an E6X, for example, has a KOEO (Key Off Engine Off) draw of more than 80 mA, the DME will set a DTC.

Also, always remember to check for TSBs for service instructions and module software updates for issues you might not know you’re dealing with.

 Here, a lab scope and an amp clamp are connected to a 2005 BMW 330I to test how long it takes the modules to power down. Lab scopes offer us the opportunity to “set it and forget it.” We can see at what time intervals modules go to sleep by putting the lab scope into deep record.

Here, a lab scope and an amp clamp are connected to a 2005 BMW 330I to test how long it takes the modules to power down. Lab scopes offer us the opportunity to “set it and forget it.” We can see at what time intervals modules go to sleep by putting the lab scope into deep record.

Lastly, keep in mind that you are working on a BMW! One of the things we need to understand when diagnosing a battery draw is that it might take half an hour or more for all the loads that the vehicle’s computers may be keeping alive to be turned off. Depending on which model you’re working on, KOEO battery drains will vary. Having the right tools and equipment such as an amp clamp and lab scope can make diagnosing a parasitic draw easier.

 Is this a good or bad KOEO battery drain? Take note that each mV equals 100mA on the scale, so we have over a 1 amp current draw.

Is this a good or bad KOEO battery drain? Take note that each mV equals 100mA on the scale, so we have over a 1 amp current draw.

Testing for parasitic draw after setting up the lab scope is easy. Simply check amperage and start pulling fuses. While using a lab

 

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Category: Electrical, the bimmer pub

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