Strange Charging problem
 

08 E320. New to Mercedes, but not wrenching. The car doesnt charge, but if you disconnect the battery and hook it back up it will charge for a while, then stop again and battery voltage will drop till things start turning off. Disconnect the battery, jump start it and it will be charging at 14v again. battery is AGM and less than a year old, alternator replaced twice. What am I missing?

Does this car have the Aux battery and if so where is it. Its not under the charcoal filer.

No aux battery on a 2008.

Thanks

what brand of alternator did you purchase?

Did you get battery tested?

Valeo

Yes, several times.

My thought right now is either the DME or imoilizer is not energizing the exciter circuit after the car has been turned off (possibly with setting the alarm).

I would get a bosch or oem alternator these cars are pretty suborn about their alternators.

sounds like your left with questionable battery ? if you really want to confirm you could put a temp battery in there or borrow a known good one if you have another car.... rig a multimeter inside or under the wiper to watch it real time.... just tossing stuff out there....

My thought right now is either the DME or imoilizer is not energizing the exciter circuit after the car has been turned off (possibly with setting the alarm).

Wiring diagrams would help.

You are probably right but I thought valeo was oem?

Trying to source another battery to borrow.

Turns out problem was alternator. Replaced with New Valeo unit.