Please help w/ "Undervoltage Consumer" message
 

My C240 is displaying the Undervoltage Consumer message after roughly 15 min of driving. The message then clears and at the end of drive there are no faults stored. I removed the alternator and had it tested and it functions OK. The car starts and runs OK, so the battery appears OK. Since this message is priority 1, should I take it seriously. Please help me to solve what might cause it.

Thank you.

Alternators can be intermittent. I have had several that run for a while and then have voltage regulation problems. I have seen them have high voltage and others go low after they get hot. Often times it is the electronic voltage regulator portion of the alternator. Other times it is the diode rectifiers that get funny when hot.

Measure the voltage at the alternator when it is having the problem. If it is less than 13.2v you can say for sure that the alternator is the problem.

Dave,

Thanks for the response. I think, it's gonna be almost impossible to measure the voltage at the alternator, as it is really burried (especially the back w/ wiring). Would it help measuring at the battery?

Yes that will work. However it does leave a few components in question such as the connections between the alternator and the battery such as cables, ground connections. These components are usually very reliable so I suspect that the alternator is the cause of your troubles.

What year???? many(most) of the 2002-2005 cars are involved in a voltage regulator recall.

MB DOC, it is 2001- first production year C240 w/ 80k miles. What puzzles me is that I did not get the specific alternator not charging message on that overcomplicated message system in this car. My battery is also original.

Thanks, dpetryk.

I think my problem is undercharging to the point that it almost killed the battery. I rad about similat case in the G-class, where the system displayed the same message (undervoltage) and when the battery was completely killed, it displayed the alternator/battery problem message....too late I guess.