M-Class (W166) Produced 2012-2015

Aucillary Battery malfunction

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Old Jan 24, 2024 | 02:23 PM
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Auxillary Battery malfunction

Starter the Ml350 2015 (gas) early in tyhe morning with Temp 8F (wc -4) suddenly warning appeared .. check coolant level. After I deleted that another warning came in AUXILLARY BATTERY MALFUNCTION. DID THIS appear because ite is so cold after driving around for 1 hr or late in the afternoon temp went up to 35F . Istarted the car again , it went fine no warning no battery malfunction now batteryand no coolant warning . for the past 3 days everything wrnt fin no warning. Any experienced this . I konw battery is affected by temp.. but wpuld it be this bad. Thanks for comments

Last edited by histo12; Jan 24, 2024 at 03:46 PM.
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Old Jan 24, 2024 | 03:11 PM
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It could be temperature-related, but I would take it as a sign the battery is on its last legs since I bet it did not happen in previous winters, correct?

https://www.batteriesplus.com/produc...IaAry4EALw_wcB

https://www.amazon.com/Genuine-000000004039-Mercedes-000000-Battery/dp/B007XRBCAK/ref=asc_df_B007XRBCAK/?tag=hyprod-20&linkCode=df0&hvadid=312430092407&hvpos=&hvnetw=g&hvrand=4287110707496937217&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9012120&hvtargid=pla-571313375036&psc=1&mcid=3f7a543ea29932fcb0262ef25e5e75af&gclid=Cj0KCQiAh8OtBhCQARIsAIkWb69yYwJ9Jfvw9mXrJXaYJKKY95OQKtKALIz34_fmyyac-DpgXTjLEV4aAsdhEALw_wcB https://www.amazon.com/Genuine-000000004039-Mercedes-000000-Battery/dp/B007XRBCAK/ref=asc_df_B007XRBCAK/?tag=hyprod-20&linkCode=df0&hvadid=312430092407&hvpos=&hvnetw=g&hvrand=4287110707496937217&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9012120&hvtargid=pla-571313375036&psc=1&mcid=3f7a543ea29932fcb0262ef25e5e75af&gclid=Cj0KCQiAh8OtBhCQARIsAIkWb69yYwJ9Jfvw9mXrJXaYJKKY95OQKtKALIz34_fmyyac-DpgXTjLEV4aAsdhEALw_wcB

Last edited by JCM_MB; Jan 24, 2024 at 03:14 PM.
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Old Jan 24, 2024 | 03:48 PM
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Yes First time,
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Old Jan 25, 2024 | 08:52 AM
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Mine will do the "Check Coolant" message when cold from time to time (full and fresh, so not sure why it does it), so I suspect that is normal so long as your coolant is reasonably fresh and topped off. Cold temp degrades battery voltage, so that could cause the other warning, but if your Aux Battery is more than like 8 years old, I'd replace it because that would be a sign it is getting weak. Batteries on the W166 last longer than regular cars probably due to the OE quality (Bosch I believe is the real brand) and most importantly, they are in a climate controlled environment, not under the hood (main battery under the right seat, aux in the rear). Replace both main and Aux at same time...they tend to have similar lives, and MB is real sensitive to voltage variations.
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Old Jan 29, 2024 | 12:30 PM
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Originally Posted by Leetom
Mine will do the "Check Coolant" message when cold from time to time (full and fresh, so not sure why it does it), so I suspect that is normal so long as your coolant is reasonably fresh and topped off. Cold temp degrades battery voltage, so that could cause the other warning, but if your Aux Battery is more than like 8 years old, I'd replace it because that would be a sign it is getting weak. Batteries on the W166 last longer than regular cars probably due to the OE quality (Bosch I believe is the real brand) and most importantly, they are in a climate controlled environment, not under the hood (main battery under the right seat, aux in the rear). Replace both main and Aux at same time...they tend to have similar lives, and MB is real sensitive to voltage variations.
what size is auxillary battery ?T he small one noooooooo4039, around 2in. in width and 3-4 in length with insertable connection with no bolts. Called dealer trelling that it is the medium one using bolt not inserted like the 0000004039. smallest one. Some in Utube sayimg AUX is with the main battery below the front passenger seat. I believe you bec I went to look taking out the opening below the 12v connection and saw + sign and a bolt ,width 2-3 inch. Did you sliced the carpet or board to replaced .AUX bat.. Thanls histo12
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Old Jan 29, 2024 | 02:09 PM
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2013 ML550 US spec. Air+Offroad pkg
Mine was the small battery with insertable leads under the right rear tail-light. Took rear of car apart to get to so not cutting anything. I've heard that MB uses different batteries at different times and puts them in various locations based on the equipment on the car, so probably best to locate it before you buy a new one. Id check under the tail light first...I think you can stick your hand down there via the access panel to see if it is there...probably need some disassembly to actually remove it...it has a bracket holding it down, hard to get to thru the access door.
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Old Jan 31, 2024 | 01:23 PM
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2013 Mercedes GL350 Bluetec (X166) & 2019 Mercedes A220 (W177) & Retired 2008 Mercedes C300 (W204)
See this thread on the battery replacement. https://mbworld.org/forums/m-class-w...x-battery.html

As previous post mentioned, double check your battery size before you buy it.

You should be able to open the access cover on the right side of the cargo area and get a phone to snap a picture of the battery in there or just open it up and get a good look (you would have already done about half the work to get access to it).
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