BMW Questions? Ask a BMW Repair Expert for Answers.
I have dealt with many power issues like this one. At times the draw can be sporadic or might not show on a conventional draw test. The test that works best is to have the dealer hook up the oscilloscope draw test. This writes a graph of the vehicle entering sleep mode and shows all wake ups and draw states over time. The dealer should drive the vehicle first, get it hot, use all of the electronics and then hook up the test. This will show if modules are not shutting down or going to sleep correctly.
The most common failure causing a wake up and draining the battery is the TCU or telephone control unit. This often will keep the rest of the vehicle awake. The other two items that are common are the power module and electrical fan for the engine causing high drains and bringing the battery down quickly. While it could be other components these should be unplugged first to try to eliminate the draw or wake up problem.
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