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Pete
Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 28767
Experience:  Over 15 years experience as a Mercedes dealer technician
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I have a 2009 c63 w204, the red battery light has displayed

Customer Question

I have a 2009 c63 w204, the red battery light has displayed on the dash, the stereo turned itself off and wouldn't power back on, then I was getting rear tail light faults then finally abs malfunction and loss of power steering, so I then pulled over and turned the car off. I then went to restart and it was completely dead. I was thinking it was the battery so I had it replaced, I checked the voltage at the battery whilst the car was running 14.1 volts, all seems well. Then once the car was warmed up the red battery light came on yet again, at this point I just drove the car home. Once home I checked the voltage at the battery and it was at 11.3 volts and was not charging at all. So now I have a new voltage regulator on order and arrives in 2 days. But I've seen a previous article where it was the x4/10 fuse block. Do you think this could also be the issue with my car? What causes this? My car does have 124 000 kms, so would the age be the cause?
Submitted: 3 months ago.
Category: Mercedes
Expert:  Pete replied 3 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

It does sound like power shut down has been occuring.The computers will start to power down electronics that are not necessary to run the vehicle when low voltage occurs like the radio.Then you saw faults for other components acting up which is a result from low voltage.

You are on the right track here as it does sound like the battery is not receiving the charge to keep it maintained above 12 volts.Usually it is the voltage regulator that causes this fault intermittently acting up needing replaced.The other component is the battery current sensor which is at and part of the ground cable at the battery.If the voltage regulator does not resolve this issue here then the sensor needs replaced.

You can also have the fault codes checked in all computers with a scan tool or computer that will plug into your vehicle to read all computers to see what codes are set.Once this is done if any codes are set ( as there can be a code set for the current sensor at fault ) that code will need diagnosed to locate the issue.

Voltage regulator and battery current sensor on this particular year and model as the most common faults.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 3 months ago.
Ok I will touch base in 2 days to confirm if it's the voltage regulator (although the current one appears in good order with plenty of life left in the brushes). I'm hoping it is the voltage regulator but I fear it may not be.As for the batter current sensor, is that part of the negative cable in the boot? Can this be replaced?
Expert:  Pete replied 3 months ago.

That is part of the negative cable in the boot at the battery itself.It usually has to be replaced with the battery ground cable assembly.Since the regulator brushes look o.k. it may be this sensor as the cause.One other item is the alternator itself needing replaced.Even if the regulator is o.k. it can fail with the magnetic pull the alternator generates to aid with charging,I have seen this before and had to replace the entire alternator assembly.

Let me know if you need anything else and feel free to rate my help here or above as this is how I receive credit for my time.Your 5 star rating is appreciated.Rating my help will not close out your question and we can continue here whenever needed still.

Thanks Pete

Customer: replied 3 months ago.
It was the voltage regulator so I wasted $60 on what I had already ordered the part last week. Part was fitted today and no more problem
Expert:  Pete replied 3 months ago.

That is great to hear.Usually it is the voltage regulator.I see you came here and asked after you had already ordered it looking for more possibilities which I had suggested just in case the voltage regulator did not correct this fault.If there is anything else I can help with let me know.

Let me know if you need anything else and feel free to rate my help here or above as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete