What does the "undervoltage consumer defective" message mean? Is it serious?
2002 Mercedes-Benz C320
Either your battery is pretty flat or the charging system is not keeping up. Need to test the charging system and charge or replace the battery if needed. Most times the battery is weak and the extra charging capacity is needed to attempt to recharge it
How do you test the charing system?
Either a VAT40 or Midtronics style tester. Oddly enough, AutoZone will test it for you for free but, I'd not have a lot of confidence in the interpretation of the test.
OK to drive the car until I can get it in?
Thats a loaded question. If it is charging then it'll be ok, if its not charging it is going to leave you stranded. However, if the consumer shutoff if the only warning, odds are it'll be ok for a little while. Would I drive it to Cali? Nope, across town, sure.
25 years on MB, diagnostic tech and trainer.