We were called to diagnose a Mercedes W164 with a typical parasitic drain which would kill the battery within 3-4 days.
The current draw ranged from 130Ma to 200Ma, but, as usual, we first scanned for DTCs which yielded in low-hanging fruit.
The next step in our test plan was to check for voltage drop.
With this inspection and with the help of thermal analysis, it was found that the alarm siren module kept waking up which proved why the draw varied from 130Ma-200Ma.
Upon disconnecting supply to the module, and monitoring the draw, the current draw dropped less than 30Ma which is within spec, the client was informed of our findings and was delighted to have the issue sorted.