Cintoman's former 2005 MB C230k.
Approximately 140,000 miles on the clock at this point.

Had the car home from College on Friday to replace the rear sway bar, bushings and links and to get a new key fob from the dealership.
Did a 500 or so mile roundtrip and on the way home, had a small hiccup.
About 90 minutes into the 2.5 hour return trip, the radio and instrument lights flashed off and then the wipers cycled. After a little bit of time, my son and I wondered if it was all in our head. But then it did it a second time.
As we pulled into our driveway, the red Battery/Alternator Visit Workshop light came on.


Car turned over strong and started right up this morning. I tested the battery with a battery test tool and indicated that the battery was strong.
Next step was to check the belt. I'm not sure how much tension there should be, but I recently had the tension pulley replaced and the belt inspected. My inspection (novice as it was) didn't reveal any issues.
Next step was the confirm battery voltage under no load and after starting. I had a reading of just over 12 volts before starting and the volt meter didn’t budge much after start-up. I gave it some throttle and made sure radio/fan was off and I couldn't get it to budge past 12.3 volts.



Is this enough to definitively identify voltage regulator or alternator failure?

My instinct is to replace the whole alternator...I've had my suspicion that the pulley was too noisy and figure that this should solve the whole issue. Plus, I've never fooled with alternator refurb.


Assuming the alternator is the problem, how simple is the DIY?
And which alternator do you recommend?


I've read some threads that suggest that Bosch and Valeo are interchangeable while others insist that I stick with what's currently in there.

I'm seeing availability at the following sources:

eeuroparts has a new Bosch for $254.29, refurb'd Bosch for $225.49 or rebuilt MB for $417.43

rmeuropean has a rebuilt Bosch for $275.35 or new Valeo for $351.24

autohausaz has rebuilt Bosch for $243.06 or new Valeo for $345.70

Napa lists NAPA Power Premium Plus "Bosch style" or "w/Valeo Type" for $204.87



I typically use ECS, FCPEuro and RMEuropean for my BMW and MB parts, but I've also had good luck with Eeuro and others.
Just checked and RockAuto has options, too. New Bosch for $222.79, new Valeo for $271.79, Remy Valeo for $186.79, Remy Bosch for $192.79.

 

Hi @VTMike , it most probably points to a faulty alternator. have it tested before replacing the battery. However, the alternator should charge the battery to 13.8 volts...

 

Thanks, Leonrsa.

Just wrapped up addressing this tonight.
I DID end up replacing the alternator. I ran into a hiccup or two (split EGR hose, my elbow hit/broke the expansion tank line as I tried to wiggle the alternator out, and then the new alternator pulley seized and I decided to replace the serpentine belt, too). The pulley seizing was due to inadvertently installing it upside down. I matched the plugs on the back because assuming that would be right. To my eye, the mounting holes were nearly symmetric. Turns out that was wrong. So I've now installed/uninstalled the whole shebang 4 times.

Again, the good news is that it's running well (even quieter than before) and I think/hope that we're in great shape now.

 

I am happy that you got it sorted...hopefully