Hello,

I have a 2012 E550 Coupe. The cigarette lighters and the USB port have extremely low voltage. The battery, alternator, fuses are all good. None of the other car systems are affected.

I will note that the drivers side seat cooler turns off after 10 seconds but I don’t think that is related at all.

Anyone have any thoughts? Thanks!!!

 

Seems odd. I would make sure the cig fuse is both good and reseated. If still a fail, what is the voltage and can it provide any current?

 

All the fuses are good. The amps are really low and the volts are also low. Power is still there but barely.

 

That low voltage and current make me suspect the fuse is blown but it's getting in some other way. For example, possibly, it might be getting through a relay winding. So you'd get something and virtually no current like you're seeing. Or a resistor or some other device on that circuit that is somehow doing similar.
So I would not just check the fuse with a mutimeter and/or eyeball, but really check it or replace it to be certain, considering the unusual circumstances.
And of course be sure it's the correct fuse. Of course I've never made that mistake :p So having screwed myself in the past, I'll circle back and double check all the stupid stuff before I start digging in deep.

I would put a load on the fuse at the fuse to be sure both the fuse is working and the circuit feeding it is working. I use an old school reverse light with wires soldered to it because they draw 2A. It's primary use is a light source for working on cars but multi-purpose.
If all fails I guess I would disconnect the batt and feed 12V into the cig lighter and see if it makes it to the fuse. Could be the cig lighter itself, or rather the wire/terminal on it. I've seen the wire cook right at the terminal and if there was just a little bit of burnt wire left, or maybe even just the carbon, it would give you a reading. For example if you used it to charge the car, charge another car, use it on a tire air compressor or anything high load for a period of time.
Or, depending on how you're reading the voltage, it could be a bad ground. I believe Benz has a good solid ground on the cig lighter but it's still another wire and two connections to fail.
I also wonder what converts the 12V to 5V for the USB? Perhaps 12V goes to this device and from there it goes to both the USB and cig, and if it fails it somehow takes out 12V too? Maybe you need a schematic to assist in this case...