Hi Long time member mostly reader. Please help is you had a similar issue as everyone is striking out in resolving intermittent engine cut out problem.
2012 GLK350 4matic 150K owned since new. It's been a trooper until now. A few months ago I had a couple situations when the engine would die at a stop light. You could put it in park, start and go without issue. No MIL no codes in the computer. Now a few months later this has happen repeatedly and often.
But now after the car shuts down, still no MIL on the dash but I get stored codes that vary. Most times it's no ground to MAF, no ground to ECU, sometimes no ground to Cam sensors etc. And just recently car went into limp mode while driving. Same situation, pull over shut down, restart car drives fine without any MIL on the dash, but has stored codes. I have a couple of instances of throttle loss but I pull over shut down, restart and car runs fine. Hot or cold, wet or dry no difference happen both when cold and warm or dry/wet. Recently has just shut off in the morning after initial start after about a minute or two of idling. Car has never shut down totally when driving only when stopped. Car usually cranks fine once the ignition is cycled On occasion you have to wait a minute for the car to start again. It only recently has had the throttle loss while driving and limp mode issue. After the first time limp mode issue today, the car showed traction stability control codes stored.
Car runs as usual when not stalling or limping.
It's driving me nuts. My Indie MB and Euro specialist has had it three times and doesn't know what to tell me.
Have tried so far:
New Battery
New Mas Air Flow
New Power Relay
New Crank Position Sensor
Tried replacing the ECU with a flashed replacement ECU same issues persist
Codes were cleared after each "fix". Not all codes return. Most common code that returns is the no ground to MAF and no ground to ECU.

Thanks in advance!

You didn't provide the codes you mentioned, which is important for analysis. You mentioned "ground" problem ... yes, that can cause many intermittent issues, even if they're unrelated. Need codes.

Thanks for the quick reply. These are some of the past XTool codes reported. There have been others. Not sure if they are the same as "Star diagnostics" . Thanks in advance.
1347 Mass air flow sensor 1 has a short circuit to ground.
OR
1347 Mass air flow sensor 1 has a short circuit to ground.MIL ON&Stored&Current
0868 The control unit has a malfunction.MIL ON&Stored&Current
1108 The power supply at the input of the control unit ''combustion engine'' has a malfunction.Stored and Current
0224 Adaptation of the idle position of the throttle valve actuator was not performed.
or
1347 Mass air flow sensor 1 has a short circuit to ground.MIL ON&Stord&Current
0868 The control unit has a malfunction.MIL ON&Stored&Current
1108 The power supply at the input of the control unit ''combustion engine'' has a malfunction.Stored and Current
0224 Adaptation of the idle position of the throttle valve actuator was not performed. Stored
B182811 The output for remote trunk opening has a malfunction.There is a short circuit to ground.
or
1347 Mass air flow sensor 1 has a short circuit to ground.MIL
0868 The control unit has a malfunction.
1108 The power supply at the input of the control unit ''combustion engine'' has a malfunction.
0224 Adaptation of the idle position of the throttle valve actuator was not performed. Stored
2182 Mass air flow sensor 1 has a malfunction. \
Audio Command
953D Signal ''Low voltage differential'' has an open circuit.
or
ESP
C320100 One or more signals sent from control unit ''Combustion engine'' via the CAN bus is implausible. Stored
C226400 One or more signals sent from control unit ''Combustion engine'' via the CAN bus is implausible. Stored
C326600 Consequential fault
ME
0200 The throttle valve actuator has a malfunction.
Audio Command
953D Signal ''Low voltage differential'' has an open circuit.
Battery Sensor
B182811 The output for remote trunk opening has a malfunction.There is a short circuit to ground.

First thing I'd do is trace, clean and tighten all the negative wiring from the battery to all the major ground points. Likewise the positive wiring from the battery to all the major distribution points. Pay close attention to the jump point.

Exactly !!

Also, if you've had a recent bout of low battery voltage (dead or nearly dead battery), it could cause issues like that. Generally you can tell for sure by resetting the codes and then seeing if they come back (or not) after the battery is sorted.

Are you sure the battery is charged ? Alternators and regulators fail, cables corrode.

Thanks for the suggestions. No battery issues (new), alternator charges at full capacity, no noticeable power draw on volt meter or lighting etc I assume it is a grounding or connection issue somewhere. I was hoping someone else had a similar issue and could point me to the trouble spot. I guess my issue is not so common.
I don't have a good wiring diagram for the GLK (and limited time) to be poking around with a multimeter, that's why I brought it into my usually solid Indie MB guy. Unfortunately, I am on visit 4 during the past month.
And, I already would have done what he did without the added six hours of labor cost with no resolve.
I will hope for a slow day at the garage where he can have a tech spend a little time tracing, poking and tightening some connections more thoroughly.
If anyone else has an idea, THANKS IN ADVANCE!