C300h no Start/Stop
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Newbie
Joined: Jun 2021
Posts: 10
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C300h
C300h no Start/Stop
My C300h Hybrid seems to work fine but the hybrid part seems to work mostly when accelerating when the car starts mostly of the time starts with engine and on traffics when not moving the car dosnt stop to save fuel, but otherwise all others work fine.
I searched and seems that the Auxiliary Battery is the main cause for this issue, I wanted to know how hard can such thing to replace my self and is the location same as a c300? or its on a different as I cant find anywhere anything that says soo.
And maybe just charging it coud that fix it or needs replacment at all?
I searched and seems that the Auxiliary Battery is the main cause for this issue, I wanted to know how hard can such thing to replace my self and is the location same as a c300? or its on a different as I cant find anywhere anything that says soo.
And maybe just charging it coud that fix it or needs replacment at all?
Super Member
Joined: Dec 2016
Posts: 797
Likes: 141
2018 C43
Your car probably have different system. I would look into why the hybrid system isn't kicking in more, perhaps due to lack of charging. Is the car sitting in the garage more? To charge the hybrid battery, the car probably runs it's engine more. Is there was to charge the hybrid battery with external charger?
Thread Starter
Newbie
Joined: Jun 2021
Posts: 10
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C300h
Your car probably have different system. I would look into why the hybrid system isn't kicking in more, perhaps due to lack of charging. Is the car sitting in the garage more? To charge the hybrid battery, the car probably runs it's engine more. Is there was to charge the hybrid battery with external charger?
Super Member
Joined: Dec 2016
Posts: 797
Likes: 141
2018 C43
What does 12v car battery reads? And how old is it?
On regular w205, eco start/stop isn't functional when the battery is under 80% and you already know about the aux capacitor.
So I am thinking similar principal applies to the hybrid, because yours is usually at 60-80%, eco start stop not kicking in.
Do you remember what the hybrid battery level was usually at when the car was brand new?
On regular w205, eco start/stop isn't functional when the battery is under 80% and you already know about the aux capacitor.
So I am thinking similar principal applies to the hybrid, because yours is usually at 60-80%, eco start stop not kicking in.
Do you remember what the hybrid battery level was usually at when the car was brand new?
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Joined: Jun 2021
Posts: 3
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From: Hertfordshire, UK
C300h, AMG Line, Premium Pack in Obsidian Black Metallic.
I take it you’re in “C” comfort or “E” eco, as the independent hybrid drive doesn’t work in “S” or “S+”.
In my preferred “C”, it starts and runs up to about 15mph (on light throttle) before the diesel engine starts or cuts in. The exception is ambient temperature extremes when either high A/C or heat in the cabin is required. Otherwise, pressing the start button, you get the green “ready” light and off you go, on electric motor.
In my preferred “C”, it starts and runs up to about 15mph (on light throttle) before the diesel engine starts or cuts in. The exception is ambient temperature extremes when either high A/C or heat in the cabin is required. Otherwise, pressing the start button, you get the green “ready” light and off you go, on electric motor.
Last edited by UKEngineered; Jul 4, 2021 at 03:40 PM.
Thread Starter
Newbie
Joined: Jun 2021
Posts: 10
Likes: 0
C300h
What does 12v car battery reads? And how old is it?
On regular w205, eco start/stop isn't functional when the battery is under 80% and you already know about the aux capacitor.
So I am thinking similar principal applies to the hybrid, because yours is usually at 60-80%, eco start stop not kicking in.
Do you remember what the hybrid battery level was usually at when the car was brand new?
On regular w205, eco start/stop isn't functional when the battery is under 80% and you already know about the aux capacitor.
So I am thinking similar principal applies to the hybrid, because yours is usually at 60-80%, eco start stop not kicking in.
Do you remember what the hybrid battery level was usually at when the car was brand new?
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Super Member
Joined: Dec 2016
Posts: 797
Likes: 141
2018 C43
I would start with cheapest repair first. Diagnostic fee, new 12v battery, aux capacitor (doubt your car would have this because it has hybrid battery). Look into charging system like the alternator and DC converter/charger for hybrid battery. I would think that won't be cheap replacing the hybrid battery or it's charging system. I didn't include starter because you never mentioned you had problem starting up in the morning.
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Newbie
Joined: Aug 2025
Posts: 1
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W205 C300h
hello,
wont to create new post, so writing in here..
have w205 300h and still cant to fix issue with eco start/stop function .. its still not working at all like hybrid system too...
i have changed:
both new battery's (but aftermarket)
main battery terminal with sensor
aux battery relay
decoupling relay
but in the cluster BN rate cant to reach 100%, max is 92%.. second BN reading in eco mode is 11 max ..
BN in the cluster shows aux battery or main battery readings?
xentry doesnt show any faults...
try to change front SAM? CDU?
wont to create new post, so writing in here..
have w205 300h and still cant to fix issue with eco start/stop function .. its still not working at all like hybrid system too...
i have changed:
both new battery's (but aftermarket)
main battery terminal with sensor
aux battery relay
decoupling relay
but in the cluster BN rate cant to reach 100%, max is 92%.. second BN reading in eco mode is 11 max ..
BN in the cluster shows aux battery or main battery readings?
xentry doesnt show any faults...
try to change front SAM? CDU?
