Hi Newbie to site and My first Merc love the car but battery drain getting me down, checked with multimeter vehicle has drain of 1.56 amps obviosly enough to drain the battery overnight, carried out checks on individual circuits found comand unit current to be 0.90 amps ( can hear fan running constantly when unit off ) This brings drain down to 0.66 amps can reduce this more by removing door module fuses and instrument cluster fuse each using 0.04 amp, i suspect the comand unit is faulty (or are they all controlled by the front sam unit maybe not shutting down ) does anyone know what the drain is on a normal functioning c320 any help appreciated.

 

Quiescent drain ball park should be circa 50 milliamp.
Plot current vs time and you should see the various computers shut down during lets say a 5 minute period.
Note: Ensure hood / trunck lid are SHUT when measuring battery drain since if open the computers will not shut down and you will not get a true reading.

Usual suspect is the battery or charging circuit.
Battery age?
Volts at battery no load engine off?
Volts at battery headlamps on engine off?
Volts at bettery engine idle no load?
Volts at battery engine on 2000 revs?
Volts at battery engine on 2000 revs headlamps on?

Please confirm you DO NOT leave the keys IN the ignition (but turned off) or NEAR the car? This prevents the computers from shutting down correctly.

Stuart