Hi all, I'm a new owner of a 2010 E350 Coupe. Long story short, a few days ago I had the car idling for about 2 hours in 90F+ degree weather. Reason for this is I was replacing the infamous comand scroll knob shaft so I had the a/c on so I didn't bake in there. Car was running perfectly fine until right around the time I was finishing the repair. I looked up at the cluster and all the lights were on. Comand screen also says auto theft mode enabled. At that point, I put the car in gear to see if it could still move - it shifted fine but the gear indicator in the cluster went blank. I also noticed none of the gauges worked (tachometer, coolant temp). I put the car back in park and tried to turn off the car but the red "Put car in Park" error came up in the cluster and would not let me shut off the car. Popped out the push start button, put the key in and turned it to the on position and the car immediately died. Tried cranking it twice and each time it cranked, started, and died immediately. At this point I tried hooking up my scanner (it's a cheap scanner but I've used it atleast 5 times since I bought this car with no problems) and it wouldnt communicate. Now the car won't even try to crank with the key in ignition.

I've recharged the battery (duralast platinum dated 10/23) at autzone and had them test it, nothing wrong with it.

Checked all fuses in both the front and rear SAM and they are all fine.

I looked for the infamous auxillary battery but turns out my car model doesnt have it i guess. I've checked behind the side panel under driver dash (theres only 2 fuses in there) and in the trunk next to the spare tire. No battery to be found and I'm not sure where else it could be.

I've explained these symptoms to close mechanic friends and they've both said it's most likely the ECU getting cooked from letting it idle in the heat for so long.

Just looking for any other opinions or advice on other things to check. Im decently mechanically inclined but I start getting lost when it comes to these kinds of electrical problems.

Edit: forgot to mention, i didnt unplug anything when i did the knob shaft repair since the car was running. I was careful to not pull on any wires so I'm positive it can't be something I did during the repair. I even tested the scroll function before reinstalling the module shortly before the car started experiencing all the issues - everything was working as intended. The issues happened between the time I tested the scroll wheel and reinstalled the module and interior trimmings.

You need a better scanner. MB-aware is best
if no scanner can communicate via the OBD2 port, the next step go old-school.

Key IN, cluster lit? Sound of steering lock motor?
Key turns?
Check voltages at the starter relay. If OK
Jump the relay with FUSED wire, if the car starts -> there is a logic control problem.
It can be theft protection, or damaged module > more diagnosis

You can try to disconnect the knob controller and to check again the fuses. The Gear Stick is not on the central console for your car, yes?