MelvinC

I have a 2012 E350 Mercedes just about 50,000 miles . Just recently I changed my main battery under the hood on the passenger side about 3 months ago due to the red light battery turning on. I changed the battery which stopped the light from popping up again. After a few months driving, All of a sudden the light popped up again but this time it's starting to command to shut off my radio and other electronic features in the car. Any advice or suggestions on how to fix this situation? I'm really hoping it's not a alternator problem. Now after a few weeks my car won't start. Sometimes it'll finally start, runs for a few seconds and then dies. Please help!!!!! I need to know what's wrong .

IgorE350

It might be alternator, i would start from that. What if you jump it, does it start?

cetialpha5

I think on the 2012, the aux battery is still in the dash. It's the one next to the driver's side door inside a compartment. Search the threads on how to change it. Otherwise it's the alternator or other charging system fault.

IgorE350

BTW what is the purpose of aux battery?

MelvinC

yea I've jumped it. Even tried to charge the battery just cause . nothing.. ever heard of a CPS? Not to familiar with that but I've read a few forums not to sure what it does....

MelvinC

where would I buy a replacement battery for that? I would try that first , but now the car engine won't even start.

cetialpha5

I think in 2014 once they had the eco mode, there was an aux battery in the trunk. But the one in the dash is for the electronic transmission, so you can still shift out of park if the main battery is dead. If it's the same one, I think someone mentioned finding one on Newegg for like $15. Search the old threads.

As for CPS, either camshaft or crankshaft position sensor. I think those normally throw a code. Is the CEL on? Even if it's not on, you might be able to take it to an auto parts store and get the car scanned for any old codes.

MelvinC

not to familiar with the aux battery but I've read a few forums , and they're stating for the aux battery it would pop up as auxiliary battery. For mine it's just the red battery box that'll pop up.

cetialpha5

https://mbworld.org/forums/e-class-w...ml#post6930867

Are you sure the main battery is charged? What's the voltage? Take it out and get it loaded test, could be a bad cell. Or you have a bad alternator, but if you take it out and charge it up, it should last long enough to drive a few miles. You could always take it out and bring it to an auto parts store if you don't have a charger.

MelvinC

so would you say the auxiliary battery would be the easy way? I am actually able to take it out of parking as well .

MelvinC

yes the main battery is charged I've checked it says 12v and it's a new battery as well. The auto shop told me it's the alternator. Some other people were telling me it can be my aux battery. My car isn't dead it just won't start , and if it does start it dies down after 2 seconds.

Zavato

At rest a charged battery should read more than 12.5 volts. With the engine running the reading should be about 14 volts.

LILBENZ230

The red warning on the dash screen showing a battery is a charging system error. It means the alternator is not charging the battery. You need to look into that.

Search dyno mode and you can put your car in it and see what the alternator is charging.

MelvinC

search dyno mode? Can you be a little specific?

LILBENZ230

https://www.youtube.com/watch?v=oFwXR19Uzno

Follow those instructions, look at vehicle data. Start the engine and it will show how many volts the alternator is charging at. You should see anywhere from 13.5-14.5. When my old W211 had the red battery warning screen, dyno mode showed 11-11.5v indicating a clear problem with the alternator.

KEY08

I would concur that you are being warned of a charging circuit issue and the dead battery is a symptom of that.

MelvinC

my only problem is I'm not able to start the car. Last time I had it checked at the auto shop. They dropped a load onto my battery, the colts indicated it was below 12v. Would you say it's an alternator problem?

MelvinC

would you say it's an alternator problem?

cetialpha5

As someone mentioned earlier, a charged battery should be in the 12.5-12.7 range at about 70 degrees. As it's winter, you may show a lower voltage depending on the temperature. If the alternator is dead, it'd make sense that the battery isn't lasting long enough to keep the engine running. You should just take the battery out and charge it fully. The car should still run even with a dead alternator and a charged battery. It's also possible you've got a couple problems going on at the same time.

LILBENZ230

You can access voltage with just the ignition on - it will give you the battery voltage.

It is a charging error, you need to address the real cause before replacing the battery again.

MelvinC

i mean the car cranks up like it's about to start. Someone mentioned to me it might be a fuel pump ?

LILBENZ230

A fuel pump will not cause the red battery warning in the cluster.

MelvinC

So what do you think it is ?

MelvinC

What is the purpose auxiliary battery?

SoCal208

MB W212 model year 2012 DO NOT HAVE auxiliary battery. Only ONE big old 12v battery (front passenger side, close to the firewall). Alternator may be your problem. Until model year 2014 > up (with stop & start in traffic that need an auxiliary battery). I can not locate any 2nd in my car, my mechanic told me my car had ONLY 1 battery.