Question about 2001 Mercedes-Benz C-Class

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2001 C240 ''Undervoltage Consumer Defective'' UNDERVOLTAGE CONSUMER DEFECTIVE come up on the dash so i did not drive the car .The next day the battery was down and so i took the battery to the garage for charging after which i put it back on, same problem. I bought a new battery and the sign went off and came back after sometime(5mins).
Just the other day i was driving and different messages were popping up... the system was going crazy, you know like it was going out of breath then the car was not accelerating so i parked by the side of the road. The car would not start after i turned it off but after about 30mins it started and i drove abit then it started showing all kinds of messages, acting crazy.What does UNDERVOLTAGE CONSUMER DEFECTIVE means. What do you think is the problem with my car thank you.

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  • Bright Amusu Apr 18, 2015

    I had exact same issue this night around 11:50pm E470 Aurora Colorado. I will tow it in the morning to the mechanic. I will give you guys the solution I came out with. My car is 2002 Mercedes c240.


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Sounds to me like a voltage regulator issue. This is attached to the alternator and monitors how much voltage is sent back to the battery. Any decent parts store should be able to hook up a charging system tool-most common is a Vat-40 and check the system. And they will probably do it for free. If there is an issue with the charging system, then try the voltage regulator first, as opposed to the alternator-there is quite a price difference I assure you. Let me know what you find.

Posted on Nov 20, 2008

  • Morad Sharif Apr 19, 2012

    Hi, I had the same problem with my E200 2002, I changed the alternator and the battery as well, but the problem remains as it was, I took it to the workshop again and they said "Alternator is fine and generates 14.6v but it seems it is not connected to the battery" can anyone advise me please?????


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I have the same problem, I've changed the alternator and the battery but the same fult apears on the dashboard again, I left the car at the workshop but they can't address the problem the only feed back I've got is "the alternator is fine and the output is 14.6v but it dos not charge the battery" and they do not know how to fix the problem.
is there anyone out there who can help with a reasonable soloution?????
it's a E200 2002

Posted on Apr 18, 2012

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SOURCE: 2001 C240 ''Undervoltage Consumer Defective''

The same thing happened to me and it turned out to be the alternator. Need to replace your alternator. Easy check, start the car and check the DC voltage of the battery, with the car running you should read around 14 volts. If you are reading 12-12.25 volts then the alternator is not generating.

Posted on Feb 06, 2009

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Undervoltage battery indicator on a mercedes c240 keeps flashing and e know that my battwry is not being recharged

check the charge rate by putting volt meter across battery with engine running if between 13 - 14 volts alternator ok ,the ecu is a completely different part to the charging system , then check if battery is holding charge at a garage

Mar 31, 2014 | Mercedes-Benz C-Class Cars & Trucks

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I got a c-class mercedes and on my dash board today appeared UNDERVOLTAGE CONSUMER DEFECTIVE. what can i do?

Check your battery and voltge when car is running if les than 12 when off than battery is flat, if less than 14 when running then it's not charging like it should.
If its charging ok and battery under 12 you need to replace battery.
If its not charging ok than it's alternator- Hope i helped!

Jan 25, 2011 | 2001 Mercedes-Benz C-Class

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Seek a advise for undervoltage/alternator or battery

measure the battery when the car is off, it should read just a little over 12V. With the car running, measure the battery again and it should read between 13V-14V+-.2V.... odds are the voltage is below 13V if that's the warning you get and the alternator is not charging properly

Sep 08, 2009 | 2001 Mercedes-Benz C-Class

1 Answer

Undervoltage light came on while driving on mb c240- light is off now...whats up?

could be battery, or the regulator pack on the alternator is failing. needs diags to be sure.
Also how hot was it when the light was on? sometimes the alternators shut down if they get very hot.

Jul 06, 2009 | 2001 Mercedes-Benz C-Class

1 Answer

Was pulling fuses and now the wipers dont work on my C240

hi,first bring your battery to battery shop,test or charge the battery,then install,check the alternator changing rate,if ok then try to fine out which consumer is consume the battery with out switching,also check the bulb or connection of trunk lightty,

Mar 21, 2009 | 2001 Mercedes-Benz C-Class

1 Answer

2001 C240 ''Undervoltage Consumer Defective''

The same thing happened to me and it turned out to be the alternator. Need to replace your alternator. Easy check, start the car and check the DC voltage of the battery, with the car running you should read around 14 volts. If you are reading 12-12.25 volts then the alternator is not generating.

Nov 18, 2008 | 2001 Mercedes-Benz C-Class

3 Answers

Undervoltage consumer defective

Regarding the first problem, there is possibly an oil level sensor issue or vehicle version coding issue(both can be more fully checked at a dealership). The second problem is not uncommon. Obviously, there could be a low voltage if the vehicle sits for a long time or is not driven alot. Sounds like the ac system lost synchronization due to lack of voltage. With vehicle running, you should be able to press and hold recirc/rest or recirc/defrost buttons on ac control panel(can't quite remember which combination). Press and hold until leds start flashing, then the ac system will go through a resynch phase. If it completes this and the led's stop flashing, then it's ok. If it does not and the led's flash very quickly, this indicates an actual malfunction of ac system adjustment motors.

Nov 06, 2008 | 2001 Mercedes-Benz C-Class

1 Answer


i have the same problem with my 2001 C240 and my a/c does not work properly as a result.

Oct 31, 2008 | 2001 Mercedes-Benz C-Class

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