Mercedes-Benz W211 battery drains overnight: finding the parasitic drain
Mercedes-Benz W211 battery drains overnight: what can cause the parasitic drain?
Culprits found have included the driver's electric seat control box (drawing over 1 A with the engine off) and, on the estate, a broken wire of the folding tow bar. The Comand unit's disc or DVD drive can also keep the bus awake and draw current.
How is parasitic drain measured and located on the W211?
Measure the current with a clamp meter that shows the direction of the current; for direct current you need a meter with a Hall sensor. In sleep mode (when the car is asleep) the reference value is below 60 mA. When the current is very high, the consumer can be located by removing fuses one at a time and watching the current drop.
Why does pulling fuses not always reveal the W211 drain?
Removing or refitting a fuse can wake up the buses, which makes the measurement unreliable. After each change, wait for the consumption to fall to the sleep level, and only then measure. If the cause is not found, have a workshop look for the fault.