My GLK 250 has a very annoying issue: the engine starts always, no problem, but I can't turn it off on 50% of cases.
The push button is ineffective for shutting down, sometimes I succeed to turn the engine off by removing the button and using the keyfob. Sometimes even that doesn't work. The keyfob battery is new.
Sometimes I just move the car back and forth, and it stops at the push button, but there is no rule.
The only consistent way is when using the key fob and waiting for a couple of minutes with the keyfob engaged and then it will shut down by itself.
The scanning didn't show anything wrong.
Any idea would be appreciated!!
Alex

What did you use to scan?

Can't say, it was a Mercedes garage, they had the real scanner, connected to the Mercedes network.

Even $50 scanner will show you a page with all the parameters needed for start.
You can reverse the reading and diagnose why ignition is not killing the fuel.
Did you try other key?

Thank you for the hint! Being a Global Express business jet systems engineer, I would say that the small presumptions are out of the equation at this moment. No scanner can compare from far with the dealer Mercedes scanner. The complexity of the Mercedes CAN-BUS protocols is not for everybody's understanding.
At this moment, I have a joint theory from two specialists, and that is a malfunction of two sensors from the front bumper, for line assistance, that might give this weird effect that I encountered. Once this issue is fixed, I will come back with news; this might be helpful for others that could face similar issues.

Do you have a horribly bad oil leak into your intake manifold/turbo?

No leak, the Mercedes dealer scanner showed 2 front bumper sensors malfunction, nothing more than that.

Did you ever discover the cause of your issue? I have the exact same vehicle and the same problem. My local dealership said they were 98% confident that updating the engine software would fix the issue and they were wrong as it persists. Prior to taking the vehicle to the dealership, I replaced the batteries in both key fobs, replaced the start/stop button and replaced the main vehicle battery. The vehicle always starts with a press of the button but does not always stop by pressing the button and requires insertion of a key to turn off the vehicle. The issue occurs when using either of the two keys I own.

Yes, I had it confirmed by Mercedes dealership, it was the EIS (electronic ignition switch) module defective. And because the dealer estimate for the work was outragious (as usual) ; 2165 CAD total for EIS (1218+tx) plus 3.5h work @190cad/hr. , I looked for alternatives. Finally I found an expert in Ottawa, (from KIJIJI pages), came on my driveway in Montreal, changed the EIS with a used one, reprogramed, all in 40 min (dashboard removed/reinstalled), all in all 350CAD, part and labor. Impressive service, impressive knowledge, not sure if he has the same tarrif these days. The guy is amazing.

If you would be able to share his name and contact information, I would be grateful. I tried to reach out to you on LinkedIn. You can send me a message there (or here, if that is possible).

Not sure if the guy would agree to give his personal number, but you contact him on the regular way, through KIJIJI, his name is Charlie (Charles Soori) ; the business number is in the add:
https://www.kijiji.ca/v-equipement-l...ing/1364095711
Let me know if it worked for you.