Jkurth

Anyone know where the aux battery is for the 2011 GLK350 AWD? I found videos that suggest it is next to the spare tire but it is not. I also checked next to steering wheel and near the main battery- no luck. I have began receiving the aux battery malfunction notice and want to replace it but I cant find it! Thanks in advance.

Mmr1

Mine a 2013 is in the rear to the right of the Spare hidden under plastic molding

NYCGLK

Hmm I thought 2011 would not have it. I don't have it on 2010.
You have start/stop function?

Jkurth

It is not there- I saw several videos for the 2013, all showing it there, tore my back apart and nothing....errr.

Jkurth

I do not have the quick start/stop function. The only other thing I can think of is seeing something similar in some C-Class where there is a module or capacitor of sorts under the dash in the passenger foot well. I will be driving and when the light comes on, the radio turns off (probably other items too). I just dont want to keep tearing the car apart to try to find this allusive battery if I dont have to.

Mmr1

Are you sure you actually have Auto Stop Start? Is there a button to turn it off? How old is your main battery?

Jkurth

I do not have the auto start/stop. The main battery was replaced about a year ago. I just put it on charge as it has been sitting for a while, but this light began coming on when it was still a daily driver. It has always started right up and no other known electrical issues.

Mmr1

Then you don’t have an Aux battery, do you have an AGM battery ?

Jkurth

The message that comes up on the dash is "Auxiliary battery malfunction". The battery was replaced with an AC Delco Professional AGM batter- supposedly it was a direct replacement/ surpassed oem specs. Should it have been a different battery? We have harsh winters here (Minnesota) and I do recall it not being able to start a couple times but attributed it to just being cold (gets down to -40 sometimes), however, I believe that may have been before replacing the battery... I do not recall the exact timing.

Mmr1

AGM is the best and came standard on my 2013, be sure your charger has an AGM cycle or it won’t charge to anywhere near 100%.
I dont think you have an Auxiliary battery unless you have auto start-stop so the message you received I can’t answer, I’m sure someone else here that knows this stuff will answer your question, maybe call a mb service dept and ask.

Jkurth

I charged the battery on 2 amp setting overnight and it read about 12.6/12.7 volts. Started the car and it dropped to 12.3- turned on radio and heated seats, dropped to 11.7. I am thinking I have an alternator issue as this should show over 14 (14.4ish) while the engine is running. Now time to look into replacing the alternator unless anyone has any ideas of something else....

Mmr1

My old 2013 battery is 12.3 in the morning and cranks at zero f just fine . Your alternator and battery are probably fine. Most all auto parts stores will check the alternator and battery for free in a minute .

Jkurth

If it is not the alternator, then what else could it be? Voltage regulator? There is obviously something wrong if the voltage does not increase while the car is running and drops below 12 volts once electric items are turned on. In any other car, one would immediately point to the alternator (no charge apparent while running) but you are suggesting otherwise? Are there other fuses or relays that prevent the battery from being charged while running? it looks like a pretty straight shot from alternator to battery....

NYCGLK

So when my belt snapped I have battery sign in red come up in the center screen.
Before replacing alt...check the wires from the alt or from battery. I have seen some of the wires get pretty corroded or can be chewed by animals.

NYCGLK

In my fleet that's 10+ years old with 100k+ miles I've yet to see a bad alternator even in 22 year old 911 it's original.

NYCGLK

Maybe AGM battery is the issue...

Jkurth

Wires looks good- I checked the voltage at the jump post as the wire from the alternator appears to go directly there- again, I am not seeing any increase in voltage. I thought the job of the alternator is to charge and would expect to see at least something while the car is running, but nothing. Are you suggesting that the battery may be bad and therefore will only accept a charge from the charger and not the alternator? The battery appears to change fine with the charger and will hold that charge so long as it is not being used. Naturally, there is a draw while the car in in operation, however, the power that is being used is not being replaced.

While looking into this, I have seen other MB owners (different engines) suggest the voltage regulator could go bad, which is on the alternator. I am starting to think that may be it if the alternator itself is unlikely to go bad, the wires appear to be good, belt is still in tact (tension looks good too) and the battery will charge/hold charge when car is not on. Unfortunately, it looks like the only way to get to the regulator on this car is to remove the alternator, so perhaps I will try that this weekend. Just hoping for anything other to check, however, it looks like it should be a pretty straight forward job. Any advice there?

Mmr1

With 12.6 I don’t see a battery or alternator issue, what are you expecting? I see a confusion with your dashboard saying You have a bad secondary battery and you don’t have a secondary battery

NYCGLK

12.6 is low with car running. Should be at 14V

NYCGLK

If I recall correctly, alt removal is not that hard. We had to remove it to get to the engine mount. 2bolts I think. I only used MB battery on my GLK. Not sure if for some reason AGM is not compatible, but not sure why that would be the case as it works in other cars.

Maybe it is bad alt...remove and take to autostore to test.

Mmr1

Get the battery tested

Mmr1

They will also check the alternator , most any auto parts store will do it free and quick

Mmr1

The terminals could be full of corrosion if the person that replaced it didn’t treat them

Jkurth

I decided to remove the alternator and check the voltage regulator and it was fried. I replaced the alternator and no more aux battery messages and the radio does not shut off now!

However, I did run into an issue. While putting the alternator back in, it looks like I ripped a wire or two, which appear to be going to the oil pan. I am receiving a message to check engine oil at next fuel stop. I took the belly pan off and sure enough, I see a broken wire (single yellow) coming from the oil pan. I began looking for the other end of it in hopes that I could just splice it back in, and although I did find another bare yellow wire, it does not appear that they are the same. The plug that goes into the back of the alternator (to the voltage regulator) currently only has one wire coming out of it (black heat shield, black wire inside it. There are 2 holes to accept wires into the harness but only one has a wire in it (the black wire). The black wire is in the same heat shield as the broken yellow wire that comes from the top of the engine. It is also odd because the yellow wire that is with the black wire, is not as long as the black one, so I am not sure if it should be connected to the alternator or if it was spliced with the other yellow wire (coming from the oil pan). There is only a single yellow wire coming from the oil pan and single black coming from the voltage regulator- does this sound correct and can the 2 yellow wires just be sliced together or is there something missing? I Cannot find any diagrams of these wires or the wires/harnesses themselves anywhere. Any help is greatly appreciated! Thanks!

ZZGlk

You might be able to find what you need at www.alldatadiy.com/. They have diagrams and service info for all models of the GLK. They charge a $30 for a year subscription for one vehicle and $20 for additional vehicles. I have a 2013 and looked at the diagrams. I see wiring going to the oil level switch which sounds like it might be what you are looking at, but it doesn't show any tie to the voltage regulator. The wiring and electrical for a 2011 is quite a bit different so they may or may not have diagrams to help you here. Be aware that there is a bit of a learning curve to looking at the information they present. It's not like the diagrams you are used to seeing in a Chiltons manual. The devices and wiring in modern cars is a lot more broken up because they are mostly tied together with computer I/O as the controlling device. They do have some interconnect wiring, but finding what you are looking for takes some patience. That said, I have found valuable information in the diagrams when I have been researching electrical issues. YRMV.