2003 E320: alternator or wiring problem?

Hi, my 2003 E320 (131K miles) had been intermittingly flashing a red “Battery/Alternator Stop Vehicle” light and annoying alarm sound as well as a “Malfunction Electrical Consumers Turned Off” sign. Then three days ago the “check engine” light came on; went away the next day. Then yesterday the engine completely shut down on me. The car started the today; took it to mechanic who says it could be alternator or wiring problem. Suggested I take it to MB dealer to get diagnosis before shelling out 800 bucks on an unnecessary car part. My question: should i take it to MB dealer or just replace the part? (I am not original owner; don’t know if alternator’s ever been replaced). Thanks for the advice.

Any mechanic or auto parts store can tell you if your charging system or battery is bad. A simple volt meter can tell you. !2.5 volts for the battery and 14.5 volts if the car is running.

@lisachills take it to a Benz dealer. I used to be a Benz technician for many years, and I can tell you from personal experience that there are many possibilities for your warning message:

Weak/old battery
Failing alternator/voltage regulator
Failing battery control module
Battery control module needs software update
Parasitic draw, which causes the battery to be in a perpetually low state of charge

This is that battery control module. It may be the $800 part that your mechanic was talking about.

Again, I HIGHLY recommend that you take it to the Benz dealer only, and nobody else. They have the latest technical service information and latest parts. They can easily perform any needed software updates.

If anybody tells you that you need an alternator, I also highly recommend going to the dealer, as there were some updates on the voltage regulator. Usually, the only part of the alternator that went bad was the regulator, which was fairly easy to replace. Unfortunately, like I said, it was superseded, so I’d want to get the very latest part from the Benz dealer, if that was in fact the problem. A lot of customers were pleasantly surprised to learn that a relatively cheap regulator fixed the car, versus an expensive alternator.

Thanks soooo much for the advice! The folks at cartalk.com rock!!

@lisachills You’re welcome.

Good luck.

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