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I just got a new battery from the dealer and tried putting my card in standby mode.
With the engine off it gives me an error massage "Function Unavailable. Please switch on vehicle"
With the Engine on it gives me the reverse error message, that the engine must be OFF
I kid you not
I just got a new battery from the dealer and tried putting my card in standby mode.
With the engine off it gives me an error massage "Function Unavailable. Please switch on vehicle"
With the Engine on it gives me the reverse error message, that the engine must be OFF
I kid you not
Oh that explains why your standby mode haven't been working ever, not because of the battery (although you did say your battery was bad on the other thread but that wasn't the cause).
Here is what you need to do, foot off the brake, press the ignition once, if it still say switch on vehicle, put it in accessory mode. That is the proper way to do it to allow the function to be enabled, it is not wrong that you need to switch on vehicle but not the engine, and it can't be enabled with engine on. Hence why it told you to switch off engine.
As said above, the message is correct. You need to switch on the vehicle. It doesn't say to turn on the engine. You need to turn on the ignition by pressing the engine start button w/o foot on the brake. The ignition has multiple positions. Off, 1 and 2 and engine start. I think ignition has to be in position 2, so you have to press the engine start button twice with the foot off the brake. Then once you've activated Standby mode, press it again to turn the car off, still w/o foot on the brake.
Last edited by superswiss; Jun 2, 2025 at 04:51 PM.
As said above, the message is correct. You need to switch on the vehicle. It doesn't say to turn on the engine. You need to turn on the ignition by pressing the engine start button w/o foot on the brake. The ignition has multiple positions. Off, 1 and 2 and engine start. I think ignition has to be in position 2, so you have to press the engine start button twice with the foot off the brake. Then once you've activated Standby mode, press it again to turn the car off, still w/o foot on the brake.
OP and we were trying to figure out why their standby mode was not working https://mbworld.org/forums/c-class-w...voltage-3.html, not until OP posted this image we figured it out, thanks for chiming in forum member superswiss.
The ignition has multiple positions. Off, 1 and 2 and engine start. I think ignition has to be in position 2, so you have to press the engine start button twice with the foot off the brake.
Bingo! It has to be in position 2. It was the second press I was missing. Thanks!
Thanks! My 2024 C300 was telling me I couldn't put it in standby due to low battery (car has been having electrical issues since I bought it). iIt's in (again) for a new battery. They gave me a 2025 C300 and I tried to put THAT in standby mode and got the same round robin as above. I'll give this method a try when I get my car back.
The way to do it is to get in the car, foot OFF the brake, push the start button TWICE quickly, it goes into accessory mode, and then navigate to Standby Mode and engage it.
Thanks! My 2024 C300 was telling me I couldn't put it in standby due to low battery (car has been having electrical issues since I bought it). iIt's in (again) for a new battery. They gave me a 2025 C300 and I tried to put THAT in standby mode and got the same round robin as above. I'll give this method a try when I get my car back.
Originally Posted by olddude
The way to do it is to get in the car, foot OFF the brake, push the start button TWICE quickly, it goes into accessory mode, and then navigate to Standby Mode and engage it.
Well, now it's not working again. MB Service told me to drive the car daily for at least 20 minutes, which I've been doing. The app says my battery is charged. But no matter how I push the start button, I just keep getting the low battery alert. My battery tested ok when I had it in the shop, and all they did was reset the system. Now, a few weeks later, with a full charge, I still can't get it into Standby. Back in it goes. For me, the electrics/electronics are the weak point of this car.
Well, now it's not working again. MB Service told me to drive the car daily for at least 20 minutes, which I've been doing. The app says my battery is charged. But no matter how I push the start button, I just keep getting the low battery alert. My battery tested ok when I had it in the shop, and all they did was reset the system. Now, a few weeks later, with a full charge, I still can't get it into Standby. Back in it goes. For me, the electrics/electronics are the weak point of this car.
MB corporate (through their email but only when battery is at critical level) actually recommend 45-60 minutes of highway driving, if you can't consider leaving the vehicle on a trickle charger.
Before I went to Hawaii for 10 days I drove the car around and about over two days to be sure the battery was fully charged. My app claimed it was. Yet, the night before I left, the car refused to enter Standby, with the same "battery is too low" nonsense. Figured, maybe it will start when I get home, maybe not.
So, about three days into the trip I checked the app. Battery still charged. The next day I got partially charged. For the next two days it showed partially charged. Then it showed charged again. I came home, still showed charged and started right up. I drove it around for a while, still won't enter Standby but says charged.
Gotta say, both of my Acuras didn't give me this nonsense. But, it started up, so I guess no harm no foul.
Before I went to Hawaii for 10 days I drove the car around and about over two days to be sure the battery was fully charged. My app claimed it was. Yet, the night before I left, the car refused to enter Standby, with the same "battery is too low" nonsense. Figured, maybe it will start when I get home, maybe not.
So, about three days into the trip I checked the app. Battery still charged. The next day I got partially charged. For the next two days it showed partially charged. Then it showed charged again. I came home, still showed charged and started right up. I drove it around for a while, still won't enter Standby but says charged.
Gotta say, both of my Acuras didn't give me this nonsense. But, it started up, so I guess no harm no foul.
I guess, and I guess the Acura didn't have standby mode though. That said, the standby mode is meant to cut communications with the Mercedes Me servers as that is what is draining the starter battery when away, it also turns off anti-theft, I mean, if you are parked outside, you want the alarm system to be running anyways, so no loss there.
No, the Acura would just sit there for two weeks and not tell me it had a battery issue because I wasn't driving it enough.
While I was away I turned off the MBUX and unplugged my dash cam. Car was in my garage and my son was home guarding the castle.
What I do find interesting is that the app shows charged, partial charged, and then charged again while the car is off and garaged. When I took it in to MB before and had them check it, all they did was restart the system (whatever that means) and Standby worked when I got it home. But then after a few weeks, it didn't. Which sounds to me like some sore of computer issue.
No, the Acura would just sit there for two weeks and not tell me it had a battery issue because I wasn't driving it enough.
While I was away I turned off the MBUX and unplugged my dash cam. Car was in my garage and my son was home guarding the castle.
What I do find interesting is that the app shows charged, partial charged, and then charged again while the car is off and garaged. When I took it in to MB before and had them check it, all they did was restart the system (whatever that means) and Standby worked when I got it home. But then after a few weeks, it didn't. Which sounds to me like some sore of computer issue.
I see. Did the acura have connected services? I assume so right if it is a modern one?
No, it only had gauges and alerts. It was a 2016. But I a 2008 as well and neither had any issues for the 8 years I had each of them. Oil changes and I think the first one had a recall but I really never did much with the service dept. I've had this MB since October and it's been in for a Check Engine Light (they reset the system) and it's been in twice for the battery alerts (they reset the system). Drives well, no issues there, it all seems to be computer or electrical, or both. The last time it was in the service mgr. shrugged and said that the computers are finicky. But I've two loaners so far. I got an extra three years of warranty, so I should be ok until at least 2030.
I feel your pain. Don't buy this nonsense about connected services. This is a bad design and a miss, not a feature of "connected services". The same people that nonchalantly tell you to just drive more wouldn't react the same if their car behaved the same way when they drive it 2 hours a day and you told them just drive less because this car is friggin connected. How about a connected Smart TV that crashes if you don't watch at least 30 minutes a day?
I drive almost daily but not enough apparently and there is always a new problem with this badly designed but connected POS.
So, to be fair, the always-on cellular connection does drain the battery over time, just like on a cell phone that's always on. Worse if you are in an area with weak cell signal, and even worse if it periodically loses the cell connection as then it constantly looks for a network to connect to. That can potentially quickly drain the battery.
Unfortunately, cars are getting more and more complicated resulting in all kinds of bugs. The 48V MHEV system throws a whole new set of complications at it. The reason your 12V battery shows partially charged and then charged again is because it gets charged via the 48V battery when it gets low. There's no 12V alternator anymore, and instead the 12V battery gets charged from the 48V side via a DC-to-DC converter. It could be that your 48V is actually getting low and preventing you from activating standby mode. You've got two main batteries and an auxiliary battery in your car.
FWIW, my 2019 C63 is always connected, but has none of this 48V MHEV BS. It sits for weeks w/o the battery getting low. I mostly only drive it on weekends, and sometimes not for several weeks. It sat for over a month during the pandemic. My battery did eventually get bad after about 5 years, which is pretty normal lifespan for an AGM battery. Now with a new battery I haven't even seen it say partially charged in the app anymore, even after it sat for a while. Last I drove it was 9 days ago and the app says my battery is still fully charged. So, definitely sounds like there are some electrical issues going on in these newer cars.
Last edited by superswiss; Jul 28, 2025 at 10:36 PM.
I've decided that it is all nonsense and, since school is about to start (It's about 15 minutes each way to my classroom), I'm not going to sweat the next two weeks before I start driving daily again. After watching and worrying about the battery, I've come to the conclusion that everything is fine and I'm just getting Mercerdes.me responses that don't matter.
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