Auxiliary Battery Malfunction
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Junior Member
Joined: Nov 2015
Posts: 29
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10 C63 AMG
Auxiliary Battery Malfunction
My car: 2015 C400
This has been discussed several times on the forums but I’m curious if it could be something else for me.
I replaced the car battery a year and a half ago.
Recently been getting the warning that there’s a malfunction in the auxiliary battery however everything that the aux battery controls is working just fine (stop/start, all heat/cooling etc no problem)
I disconnected my battery, replaced the Aux battery myself (very easy btw) and the error is still appearing. The car runs and drives perfectly fine but this error is irritating and I am wanting to sell the vehicle soon so hoping for an idea on what else I could look into?
Could it be part number: a0009050454 (battery sensor)?
I don’t think it’s my actual battery as I mentioned it was replaced rather recently and the car is always garage stored and driven daily.
Any ideas?
This has been discussed several times on the forums but I’m curious if it could be something else for me.
I replaced the car battery a year and a half ago.
Recently been getting the warning that there’s a malfunction in the auxiliary battery however everything that the aux battery controls is working just fine (stop/start, all heat/cooling etc no problem)
I disconnected my battery, replaced the Aux battery myself (very easy btw) and the error is still appearing. The car runs and drives perfectly fine but this error is irritating and I am wanting to sell the vehicle soon so hoping for an idea on what else I could look into?
Could it be part number: a0009050454 (battery sensor)?
I don’t think it’s my actual battery as I mentioned it was replaced rather recently and the car is always garage stored and driven daily.
Any ideas?
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From: Melbourne, Australia
2016 GLC 250d AMG pack, 2017 GLC Coupe 250d AMG pack , 2002 BMW 330Ci convertible, 2021 BMX X1 sD20i
Do you have an ODB2 reader to read any error codes?
You may need to clear all error codes, go for a 15-30 minute drive and see if it returns.
Not sure re battery sensor.
let us know how you go. Good luck.
You may need to clear all error codes, go for a 15-30 minute drive and see if it returns.
Not sure re battery sensor.
let us know how you go. Good luck.
MBWorld Fanatic!
Joined: Mar 2016
Posts: 1,040
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From: Melbourne, Australia
2016 GLC 250d AMG pack, 2017 GLC Coupe 250d AMG pack , 2002 BMW 330Ci convertible, 2021 BMX X1 sD20i
Hopefully with same AGM battery. 80Ah, RC140 min and 800 CCA. If not same should be higher capacity.
Also these batteries will run down due to current drain, so depending on cold or heat, should try overnight charging every 4 to 6 weeks approx to help electronics, battery and Aux capacitor.
Short daily trips will not help battery - only adds to drain, garage store helps, but you need to top up so battery is not stressed.
remote locking car with double tap helps put car and sensor/ECU’s to sleep - a lot of sensors that would otherwise be on standby and sensing if someone was around.
Good luck.
Also these batteries will run down due to current drain, so depending on cold or heat, should try overnight charging every 4 to 6 weeks approx to help electronics, battery and Aux capacitor.
Short daily trips will not help battery - only adds to drain, garage store helps, but you need to top up so battery is not stressed.
remote locking car with double tap helps put car and sensor/ECU’s to sleep - a lot of sensors that would otherwise be on standby and sensing if someone was around.
Good luck.
Last edited by Teckno; Jun 9, 2021 at 09:53 AM. Reason: Spell
Thread Starter
Junior Member
Joined: Nov 2015
Posts: 29
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10 C63 AMG
Hopefully with same AGM battery. 80Ah, RC140 min and 800 CCA. If not same should be higher capacity.
Also these batteries will run down due to current drain, so depending on cold or heat, should try overnight charging every 4 to 6 weeks approx to help electronics, battery and Aux capacitor.
Short daily trips will not help battery - only adds to drain, garage store helps, but you need to top up so battery is not stressed.
remote locking car with double tap helps put car and sensor/ECU’s to sleep - a lot of sensors that would otherwise be on standby and sensing if someone was around.
Good luck.
Also these batteries will run down due to current drain, so depending on cold or heat, should try overnight charging every 4 to 6 weeks approx to help electronics, battery and Aux capacitor.
Short daily trips will not help battery - only adds to drain, garage store helps, but you need to top up so battery is not stressed.
remote locking car with double tap helps put car and sensor/ECU’s to sleep - a lot of sensors that would otherwise be on standby and sensing if someone was around.
Good luck.
that’s the battery I replaced with. 70Ah, 760CCA and 120RC. A little less than what you quoted above. I can put it on a battery charger and see if anything changes
Thread Starter
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10 C63 AMG
I have JB4. No codes
battery was not OEM
https://www.napacanada.com/en/p/RNQ4...NriPYRNpv8SlpQ
that’s the battery I replaced with. 70Ah, 760CCA and 120RC. A little less than what you quoted above. I can put it on a battery charger and see if anything changes
battery was not OEM
https://www.napacanada.com/en/p/RNQ4...NriPYRNpv8SlpQ
that’s the battery I replaced with. 70Ah, 760CCA and 120RC. A little less than what you quoted above. I can put it on a battery charger and see if anything changes
The quality of my driving experience hasn’t changed whatsoever.
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Joined: Mar 2016
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From: Melbourne, Australia
2016 GLC 250d AMG pack, 2017 GLC Coupe 250d AMG pack , 2002 BMW 330Ci convertible, 2021 BMX X1 sD20i
I put it on my battery charger. Read “lo” left it on for 4 hours battery came back up to 90% but Aux Malfunction warning still on, not sure if it’s the main battery, unless the charge drops overnight drastically or after driving?
The quality of my driving experience hasn’t changed whatsoever.
The quality of my driving experience hasn’t changed whatsoever.
Lot of batteries sold with minimum charge in them as they may have been sitting on shelves for 4 months or longer.
Always best to charge a new battery before fitting, not always practical, or when installed in car, to have it at max capacity and take load off alternator.
Good luck, do another full, long charge and give the system a day or two. Good there are no error codes.
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Thread Starter
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10 C63 AMG
I would try to leave battery on charge overnight, around 12 hours. If intelligent battery charger it will hit battery with high rate of top up in short time, then slow down at 80% mark to not distress battery and trickle charge till 100%, then go into maintain mode, no chance of damage or overcharging. 4 hour charge from low indicated battery needs longer recharge.
Lot of batteries sold with minimum charge in them as they may have been sitting on shelves for 4 months or longer.
Always best to charge a new battery before fitting, not always practical, or when installed in car, to have it at max capacity and take load off alternator.
Good luck, do another full, long charge and give the system a day or two. Good there are no error codes.
Lot of batteries sold with minimum charge in them as they may have been sitting on shelves for 4 months or longer.
Always best to charge a new battery before fitting, not always practical, or when installed in car, to have it at max capacity and take load off alternator.
Good luck, do another full, long charge and give the system a day or two. Good there are no error codes.
still have the auxiliary battery malfunction code. I wonder if it just needs to be reset somehow
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Junior Member
Joined: Mar 2021
Posts: 63
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C300
How about the park pawl fuse in the trunk fuse box? The auxiliary battery is also called a park Pawl capacitor.
This is a good article on other causes of that message.
https://uk.autologic.com/news/support-case-study
This is a good article on other causes of that message.
https://uk.autologic.com/news/support-case-study
Super Member
Joined: Dec 2016
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2018 C43
I got the battery charged to 100%. I’ll leave it on the charger overnight. It’s intelligent and won’t over charge it. The battery was checked at a store with a battery tester and it came back “battery is good” this was however after I had it trickle charged for 6+ hours.
still have the auxiliary battery malfunction code. I wonder if it just needs to be reset somehow
still have the auxiliary battery malfunction code. I wonder if it just needs to be reset somehow
Over the years, there were few posts being successful with replacing the aux with no further error msg or it simple disappeared. Few having continuous error with the new aux replacement. One I do remember, he replaced with eBay unit and had same problem as you. Once he replaced it with oem from the dealer, msg went away. Real hit and miss.
Thread Starter
Junior Member
Joined: Nov 2015
Posts: 29
Likes: 3
10 C63 AMG
How about the park pawl fuse in the trunk fuse box? The auxiliary battery is also called a park Pawl capacitor.
This is a good article on other causes of that message.
https://uk.autologic.com/news/support-case-study
This is a good article on other causes of that message.
https://uk.autologic.com/news/support-case-study
I had an appointment to go to the dealer tomorrow but thank god for everyone’s help you saved me a couple hundred dollars!
