Make: BMW | Model Example: 2016 X3 | Avg. Mileage: 113420 | Job Number: 372188
No Power, Dead Battery
Known problem with the fan control module, which is incorporated in the auxiliary radiator/condenser fan itself, causing a current draw. Also, the blower speed controller for the heater and A/C fan can cause an abnormal current draw.
Parasitic battery draw
Load test the battery, and if it is not a sealed type, test specific gravity.
If the battery test is good, install either an inductive low-amp clamp on the negative battery cable, or the leads from a digital ammeter between the battery cable and post. If using a digital ammeter, leave the cable attached to the battery post for the time being.
If the battery is installed in the trunk, as is the case in most current BMWs, open the trunk and turn the lock to the lock position to simulate the trunk lid has been closed. Make sure the hood and all other doors are closed.
Open and close the drivers door, turn on the ignition and turn on and off electrical consumers, such as lights, heater blower and radio.
Open and close the drivers door, then lock the doors.
Remove the negative battery cable from the post if using a digital ammeter without an amp clamp, leaving the leads connected to the post and cable end. If using a low-amp clamp, leave it connected to the negative cable without removing the cable from the post.
Monitor the current draw. After 16 minutes minimum, the current draw reading should be at a nominal level of 50 milliamp or less.
Many late model BMWs may take as long as 70 minutes to reach steady state current draw minimum readings.
Be sure to disconnect the B+ cable at the alternator as this is also a known draw source.
Attempting to test current draw on late BMWs without following the above steps can lead to erroneous readings. There is a known problem with the fan control module, which is incorporated in the auxiliary radiator/condenser fan itself, causing a current draw. Also, the blower speed controller for the heater and A/C fan can cause an abnormal current draw.
By going the 9 testing steps, automotive mechanics should be able to void spending wasted time chasing down erroneous readings, and be able to focus clearly on the right fix.
Most Popular Fix:
Replaced/Repaired Blower Control Final Stage Unit – Replaced/Recharged/Programmed Battery
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Anthony attended the Dunwoody College of Technology Automotive program from 2007 to 2009.He worked at two dealerships in the Twin Cities before coming to Identifix. Anthony is an L1 certified Master Technician. He enjoys playing video games, lifting weights, and playing guitar. Anthony’s number 1 priority is his daughter.
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