Azosh422

Recently purchased a 2003 e500 for my daughter for a steal. Super clean in and out, no mechanical issues very well taken care of car. The guy before me replaced the main battery in the trunk 1 week before I bought it. But the red battery light in the dash was on so we tested the sbc battery and sure enough it's dead. After purchasing the car I replaced the sbc battery after 3 days so there are 2 new batteries in the car but the malfunction light is still there. Is there something I have to do to reset that? Or should it go away on its own? Also now that we have been driving it for a couple weeks I also noticed that sometimes the srs light will turn on when we cold start the car in the morning. But if I turn the car off and on again after a couple mins it will go away. I'm guessing that has something to do with the batttery light problem I'm having? What's going on :p

bbirdwell

Here is a quick and dirty way to check if your alternator is putting out voltage. The W211 has a power-hungry distributed digital control system that is not happy with low voltage.

Azosh422

I've seen that trick before but for some reason the car does not do that. The actually button is functional, it's just that nothing happens when I try this.

Azosh422

Even the hidden menu in the ac does not show anything. #24 is battery voltage and when I get there it has double zeros 00. But like I said there's 2 new batteries in the car. Is it the alternator?

mtrevelino

My take on this is that you have a bad voltage regulator. The alternators seem to last forever, but the regulator only about 175k miles, due to the brushes being worn. FYI, the voltage regulator is mounted to the rear of the alternator. Attached is what the regulator brushes look like new and about 60-percent worn. I did not watch the previous video on getting the voltage to come up on the dashboard, but in the worst case, connect a volt meter to the battery in the trunk to see if it is reading above 14 volts above idle.
Mike T.