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Engine starts weaker, could be an issue with the auxiliary battery?
This is a case of W205, 2017 C300 4matic sedan.
I've recently experienced two instances of Eco Start/Stop failure while driving, and I was thinking it's because of the 2years old battery but I am doubt it is caused by the auxiliary battery because..
The battery voltage measures 12.7V when idle, 14.9V while driving, and drops to around 9V on the OBD2 graph when starting the engine, but it recovers immediately (look at the image)
The battery was replaced two years ago, and I had the main battery checked at AutoZone, and they confirmed it is in good condition. However, they seemed unfamiliar with the auxiliary battery and Mercedes.
No error codes are displayed in OBD2, and there are no warnings on the dashboard.
When checking the voltage of fuse #448 in the trunk area, it shows 0V even while the engine is running?
When starting the engine while parked, it feels weaker compared to before, and the engine starts with a slight delay.
The auto start function has failed to operate twice in the past month while driving. Q1. Can there be an issue with the voltage converter(auxiliary battery) even if there are no warning indicators? Q2. Can the operation of the voltage converter be checked by measuring the voltage of fuse #448? Q3. Any ideas?
did they load test the battery ? And what battery did you put in there ?
did you have the battery counter reset ? Not resetting could cause the car to charge the battery like it’s an old battery vs a new one and shorten the life - which is something you may be facing.
a good scan tool could help diagnose secondary battery codes but that’s not an actual “battery”
I haven’t replaced the battery yet; I apologize for the confusion. I’ll edit the original post. Also, I was unaware of the battery counter, so thank you for the information.
did they load test the battery ? And what battery did you put in there ?
did you have the battery counter reset ? Not resetting could cause the car to charge the battery like it’s an old battery vs a new one and shorten the life - which is something you may be facing.
a good scan tool could help diagnose secondary battery codes but that’s not an actual “battery”
I visited and saw a mechanic, was just told that they can replace the battery if only the voltage is under very low like 2-3v otherwise the manufacturer won’t accept the warranty replacement. So they will drain the battery first when next visit. I am wondering if there isn’t any condition of voltage at loading for free replacement under warranty?
My battery is MTX 94R/H7 and it is still under warranty of 36 months
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Engine starts weaker, could be an issue with the auxiliary battery?
