paulf124

My 2003 E500 73,000 miles
is getting the battery warning message at times and is getting more frequent.
Dash lights are pulsing in brightness so I checked voltage at the main batery.
Found it varing 13.4 to 14.8 at idle.
I guess it is an alternator or voltage regulator problem.
How can I determine which one?
Is VR on the alternator like on most US cars or a seperate unit.
what is the location ?

Thanks for any help on this I hate to send it to MB it is allways so costly.

vettdvr

Mine 2003 E500 did the same thing at about 80,000 miles. I replaced the main battery with a new one from CarQuest. I did a full electrical system check on mine and confirmed the battery was looking capacity. It still started the car but under heavy load resulted in the warning. My guess is you have the origional battery and it is beginning to fail.

paulf124

Battery was replaced about a year ago.
Problem is present regardless of electrical load.
It was very intermittent but becoming more frequent.
Batt Voltage after sitting all night is still 12.4V so don't think batt is weak or not holding a charge.
I also replaced the AUX batt just because it was old but it still had a good reading.

vettdvr

1) Verify the alternator is charging.

If it is charging.

2) The battery modules that could also cause this located in the trunk by the main battery.

See attached.

3) Power seat relay under driver seat can also cause parasite power loss.

Don't underestimate that a new battery doesn't mean it is a 'good' battery. Check the 'new' battery and verify it is good.

paulf124

Can the battery modules cause the alternato output to vary up and down every few seconds?
Or is that controled bt the voltage regulator?

vettdvr

The module is not the regulator. The module is control as you have dual batteries. I have the tech details in the sevice manual.

Send me your PM and I will email you my adobe file with the information.