RBMGL550

2011 MB GL550

Not sure what happened has my wife was driving it at the time. The engine revved high, then lost power. It then appeared to go into limp mode.
Once she pulled over to a parking lot, she stopped the car. From that point on, the car in park didn't engage park.
The car in drive didn't engage and move forward. The car in reverse didn't engage and move backwards. Moving the gear shift from Drive to Park gave a brief clicking/grinding sound.

The car needs to have the emergency brake on otherwise the car will roll even though the gear shift is in Park.

I have a simple OBDII scanner and had some codes though no check engine light prior. Cleared codes and tried again. None of the codes appeared real time.

Codes which had been triggered (again, though, no check engine light, so hadn't checked prior to limp mode event)

5399 - Gear Selected from the control module 'N15/3' is implausible
P0721 - Defective Output Shaft Speed Sensor
6001 - the supply voltage of the control unit is too low

These all sound pretty ominous. Any suggestions why the transmission is not operational at all?

RBMGL550

Sounds like another thread - W204 - P0720 and P0721: car doesn’t move but engine runs smoothly

Except I don't get the codes when I shut the car off and start again. No codes at this point

vesiadog

Please read about the 722.9 transmission faults.
Questions
1. How many miles on the car?
2. How many times has the transmission fluid been changed ?
3. Has the car been thru any over heat incidences?
4. You will need to look for more error codes on more mods. I would suspect something might be going on with the wheel speed sensors.
The bare minimum reader that will help you right now is the ICarSoft MB version..$100-200
You will use it quite often . Highly advise buying one.
5. Any wheel bearings been changed lately?

RBMGL550

1. How many miles on the car?

120K miles

2. How many times has the transmission fluid been changed ?

Not during the time that I have owned the car (4 years)

3. Has the car been thru any over heat incidences?

No

4. You will need to look for more error codes on more mods. I would suspect something might be going on with the wheel speed sensors.

The bare minimum reader that will help you right now is the ICarSoft MB version..$100-200
You will use it quite often . Highly advise buying one.

Thanks. Will do

5. Any wheel bearings been changed lately?

Not recently, 3 years ago. Replace Left Front Wheel Bearing Assembly

vesiadog

As soon as you figure out what is going on with this recent error… hopefully not a serious tranny problem I would definitely get a tranny fluid and filter change asap. If you end up dropping the transmission vavle body i would change all the orings on the shift spools also.

Max Blast

If the car rolls with ISM commanding it out of park there is something mechanically wrong (pawl stripped), or ISM is unable to shift the car out of neutral.

OP mentions a crunching noise when moving the select lever, it should sound like a (for lack of a better description) hyperstretching a leather belt one shifting out a neutral into either reverse driver or park.