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Had the same problem with my 2016 GLA 250 prior to receiving a message statung "auxiliary battery malfunction". I just replaced the auxiliary battery so I am hoping that this will fix the issue. I will provide an update later. Please stay safe.
Did the problem reoccurred after replacing the auxiliary battery? Please let us know. Thanks!
 

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Hi Folks,

Just an update since my original post.

For the past 10 months, I have been deactivating the Eco-mode when I start driving so my GLA250 no longer shifted to neutral at red lights. Then recently, the check engine light came on and I was told that my main and auxiliary batteries needed replacement. After replacing both batteries by myself (dealer wanted $900+), the problem seemed to have fixed itself. I'm not sure if this will work with others', but just wanted to share my experience.

*** Tip: Make sure to plug in an auxiliary battery backup before changing the main battery under the hood (in case auxiliary battery is dead as well).

Good luck!
Hello - Please let us know if the problem went away after replacing the auxiliary battery. Thanks!
 

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Hi Folks, Just wondering if anyone's GLA has ever shifted from Drive to Neutral while stopped at a red light and NOT automatically returned to Drive when releasing the brake and attempting to accelerate. It has happened several times to my 2015 GLA 250 and I have had to manually shift back to Drive. Scary and hoping it's not a major transmission issue. Thanks in advance and sorry if this question has already been asked.
Hi Folks, Just wondering if anyone's GLA has ever shifted from Drive to Neutral while stopped at a red light and NOT automatically returned to Drive when releasing the brake and attempting to accelerate. It has happened several times to my 2015 GLA 250 and I have had to manually shift back to Drive. Scary and hoping it's not a major transmission issue. Thanks in advance and sorry if this question has already been asked.
Hey!! I have the EXACT same issue with my 2015 GLA 250. It started about 5 days ago and then yesterday, it happened again. Was changing the auxiliary battery the fix, or not driving the car in eco mode, or both?!! Please help! Im clueless with all car issues.
 

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Hi All - Same thing happened yesterday (August 13, 2022) to my in-laws 2016 GLA250. It happened twice I was told. The car shifted from Drive to Neutral while sitting at a stop light and the only way to get the transmission back to drive is to turn the ignition off and on. I’ve been searching the Internet for solution and found this site. I replaced the Auxiliary battery as some of you suggested and drove the car all afternoon today with ECO mode on. Went and sat through several stop lights and I can’t duplicate the problem. So maybe replacing the auxiliary battery is the fixed??? Question to the couple of folks on this thread that replaced auxiliary battery has the issue re-occurred since replacing auxiliary battery? Please let me know as I am a bit skeptical how an auxiliary battery controls transmission shifting from Drive to neutral. Anybody know what is happening to the transmission control module recall? I read lot of folks have experienced the same problem on their GLA250. I even went to NHTSB website and didn’t find recall or service bulletin for transmission inadvertently shifting from Drive to neutral. I also read about self voluntary recall? Is that mean I can bring the car to the dealership and have them replace the transmission control module simply by mentioning it? I’m afraid MB dealer service writers will try to upsell to my elderly in-laws and play with their safety emotions without addressing the problem.
Hey!! Did it fix the issue? Im currently facing the exact same problem with my 2015 GLA 250.
 

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Yes it Fixed the issue! I ended up buying the auxiliary battery from Napa auto parts. Dealer wants $900 so stay away from dealer go to your local auto parts store instead. Replacing the aux battery is so simple all you need is a 10 millimeter wrench. The battery is located underneath the glove compartment all you have to do is pull the carpet and remove the plastic cover to access the battery.
 

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Hey!! I have the EXACT same issue with my 2015 GLA 250. It started about 5 days ago and then yesterday, it happened again. Was changing the auxiliary battery the fix, or not driving the car in eco mode, or both?!! Please help! Im clueless with all car issues.
Yes it Fixed the issue! I ended up buying the auxiliary battery from Napa auto parts. Dealer wants $900 so stay away from dealer go to your local auto parts store instead. Replacing the aux battery is so simple all you need is a 10 millimeter wrench. The battery is located underneath the glove compartment all you have to do is pull the carpet and remove the plastic cover to access the battery.
 

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Hey!! Did it fix the issue? Im currently facing the exact same problem with my 2015 GLA 250.
Yes it Fixed the issue! I ended up buying the auxiliary battery from Napa auto parts. Dealer wants $900 so stay away from dealer go to your local auto parts store instead. Replacing the aux battery is so simple all you need is a 10 millimeter wrench. The battery is located underneath the glove compartment all you have to do is pull the carpet and remove the plastic cover to access the battery.
 

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Aux battery location (ignore number 4, from another OP member's post). The battery is adjacent the Cabin Air Filter, behind glovebox [left located driver].
Motor vehicle Hood Automotive tire Bumper Automotive design
 

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Remember, always disconnect the negative (- Black/Silver) first, then the positive (+ Red).

When restoring attach the positive and then the negative.

The Aux is of course a small/relatively low capacity 12V Li-ion but proper procedure is still that. ;)
 

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This exact issue was happening to my son's 2015 GLA250. Local dealer (Alaska) service tech said it needed a transmission control module even though my wife told them the message regarding auxiliary battery appeared and charged her $2.2K for repairs. It did not fix the problem. After bringing the car back in, they replaced the auxiliary battery and problem went away. They replaced the battery "at no cost" to us. Yeah, right...it cost us over $2K and didn't need to be done! I'd be happy to pay for the battery that actually fixed the problem. They refuse to reimburse us for the costly repairs that were not needed!
 

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2020 GLA250 4MATIC Avantgarde Edition
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I have a 2017 GLA 250 with fewer than 50K miles, and it's doing the same thing. How many of us have to have this issue before there is a recall? BJT
Doubt there will be a recall, it's a discontinued platform and doesn't create a safety risk. Low battery voltage is one of the leading causes of electrical problems. Usually step #1 with electrical issues is to charge the battery and then get it tested. Replacing it or even charging it solves the problem in many cases.
 
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