Happy New Year!

I have a 2010 GL 550. I had noticed that the 12V socket in the passenger footwell used to die/lose power supply as soon as I opened the driver door after turning the engine off, which would also kill Command. Over the past 2 months or so, I've noticed that it takes a bit longer for it to lower power supply. I have a dashcam/GPS unit connected to it so I see how the power supply behaves every time I turn the car on/off. According to the manual, the 12V outlets are powered when the engine is off, but I did not see anything about cutting power to them when the driver door is opened after the motor is turned off. The manual does mention that power to the 12V outlets will be cut if the battery charge drops below a certain level (unspecified in the manual). I had an issue with low battery voltage earlier this year and trickle charged the battery. No issues since then, but I can't be sure if the behaviour of the 12V socket in the passenger footwell changed around that time or not.

For those who have the socket (not sure if earlier year models did or not) and have noticed when it loses power supply, would you please let me know if it's immediately after killing the motor and opening the driver door? Or does it take a bit longer? Or does it not lose power at all? I have not measured mine with a timer, but I guestimate 30 sec to 1 min after I open the driver door, mine would lose power.

It perplexes me a bit that it used to behave one way and then it decided to add the delay. I am OK with how it works, although it was nice to see the GPS unit turn off when I opened the driver door, rather than having to wonder if I will come back to a dead battery if I accidentally forget to turn the GPS off, which I have tried to make a habit of.

Thanks in advance!

 

According to our user manual - and this is consistent with how my 2011 GL350 works, the plugs are supposed to always be on. If you are losing both comand and power plug voltage, I would suspect your truck thinks your battery is drained, so I would start checking voltage. It could be something as simple as corrosion or a slightly loose connection on your battery terminals, or it could indicate a problem with your battery or your charging system. But the first step would be measuring your voltage to get a better sense of whether a low voltage condition is causing your power plugs and comand to shut off...
"You can use the power outlets even if the
ignition is switched off.
An emergency shut-off feature is designed
to prevent the vehicle’s on-board voltage
from dropping below a minimum level. If
the on-board voltage drops to this
minimum level, the power outlets are
automatically switched off, to help
preserve engine starting power"

 

So it seems I may have a gremlin, then. The 12V outlet powers up when I start the car, not when I enter the truck, and powers down shortly after I shut the engine off and open the driver door. But the outlet remains powered if I shut the engine off but do not open the driver door. I will have to check the battery level to see where it stands these days.

 

Its normal. Mine does the exact same.

 

Great! Thanks for putting my mind at peace.

 

Ha ha, it’s an ISO 4165 plug ... not a cig lighter plug!

https://en.wikipedia.org/wiki/ISO_4165

of course these vehicles do not have an electrical system as we traditionally think of it, but rather have a CAN bus, which means every single electrical component is computer controlled and monitored. The computer won’t let you run your battery down.

https://en.wikipedia.org/wiki/CAN_bus

 

I concluded that the outlets remain powered on if power is being drawn when the engine is turned off. If no power is being drawn, the outlets are turned off. They are not truly always-on.

 

This is correct, except, again, they will not let you run battery down and I think they may be on a timer. Same thing as when you walk away with tailgate open ... interior light remains on for a while, then times out. Pretty sure this isn't just before battery is dead.

 

Timer seems weird, but I wouldn't put anything past the MB code engineers.

I managed to drain a battery - yeah it was weak - leaving just my phone on overnight playing music.