25 Aug Diagnosing Parasitic Draw in a BMW M5
If you have a dead battery that has recently passed a battery load test, or it’s a new battery, chances are you have a parasitic electrical draw. This issue will cause the faulty consumer to stay on long after your vehicle has gotten the sleep or shutdown signal, and can drain your battery dead in a relatively short period of time. How do we find the faulty component? By using the process of elimination, we isolate the feed circuit, then the consumer.
To find the parasitic draw, we start by opening up any areas that we may need to access during the diagnosis. Make sure to latch and trip any light triggers so the vehicle can attain sleep mode. In this case, hood trigger up, glove box light disconnected, all four doors latched and the trunk latched.
Next, we access the battery and remove the negative terminal connection. Our DVOM set on DC amperage goes in line with the negative battery terminal and the ground cable connection. One lead for each side of the connection. Once connected, we allow the amperage to stabilize for 30-60 min.
The acceptable draw for modern cars is under 30MA but can be as high as 50MA. If above 30MA, begin to isolate the circuit by removing all electrical consumers one at a time. This is done by pulling one single fuse out at a time from the junction boxes. Do not place fuse back in. Leave it out for the remainder of the test, as plugging something back in can cause a wake-up or power-up signal to be sent.
Once the fuse circuit or component is located, you will see a rapid and immediate drop in amperage indicated on the meter signaling you have located the circuit that the parasitic draw is on. Check the vehicle wiring diagram to see all additional components that the fuse feeds. Plug the fuse back in, wait at least 30 min and continue to access and disconnect components located on the circuit until the draw subsides.
Test each individual component fed by the fuse. Replace faulty component and recheck- now you’ve found and fixed your parasitic draw!
If you need help with an electrical problem on your BMW E60 M5 or any other car diagnostic issue, don’t hesitate to call us at 815-230-2900, or contact us through email at firstname.lastname@example.org. We’re conveniently located in the Naperville/Plainfield area of the Chicago Metropolitan suburbs.