Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hello,Before going into rest mode, electronic contrlol units can draw up to 10 amps when battery is connected. That's why such test is not a good indicator on this car.
so it is important to measure the draw in rest mode.
Most common causes for drain are seat control units on this model
They are mounted to the seat frame, so it's quite easy to unplug all of their connectors
Thank you for your advise stan, it's not my car, i've been asked to look at it for a relative as i used to work as an auto spark but thats 16yr ago, but things have changed abit since then! the car is also showing an srs seat belt restraint error on the dash, could this be related?
SRS ( airbag) is quite reliable and does not commonly cause any drains. But without a scan it is not possible to tell what is causing the light to be on.
Nowadays on Mercedes we have to connect the ammeter and then measure the CAN voltage, to determine if vehicle is asleep
If CAN is not asleep, control unit connectors must be disconnected from CAN distiributors to localize which ''bad child'' is keeping the kindergarden of control units awake)))
i assume the ammeter has to be connected without the circuit being broken with use of a slave battery or using a clamp on meter then
one thing i noticed was that there is a slight humming noise from were thr front interior light is
Take two longer wires. Tie one around the ground cable, and another around ground post of the battery. Connect them to ammeter leads. Let the car go into rest mode. Remove the ground cable from the post. This way a circuit is not broken. Now disconnect the plugs from the light and it will be clear if the noise is affecting the current drain