Merkey

Went to start our 2009 ML320 Bluetec with 99,500 miles, the other day and I got a red trans fault warning.

Turned off the Ignition, and restarted, and it was fine.
Then it did it again.

Diagnosed using my MB2 code reader...
4x codes.
1/ #1921 System Shutdown due to internal fault in component A80(ISM for DIRECT SELECT).
2/ #1922 System Shutdown due to internal fault in component A80(ISM for DIRECT SELECT).
3/ #1974 Selector Lever Position "P" was engaged due to a fault occurring in Component A80(ISM for DIRECT SELECT). Or The Vehicle communications
4/ #1934 The Internal Mechanism in component A80(ISM for DIRECT SELECT), For engaging selector lever Position P is not in the correct position.

I have replaced the main battery, prob 3 years ago, but have never replaced the Auxiliary Battery in the 7 years we have owned it...
No codes have ever popped up for it.
Could it be the Aux battery?

I contacted a module repair service and they said the Module has failed and cannot be fixed, and that I need to find a used one that they can clone my original and reprogram...
Thoughts or experience anyone?

BlackML550

I dont know the answer but If i were you, Id be checking both batteries especially the auxillary battery and alternator. If only to remove them from the equation. You might get lucky. If you have anything less than 13.7V engine on and 12.7V engine off, a drop on voltage can trigger fault codes. Any other codes even if they appear unrelated? Any low voltage codes at all or non communication codes? Thats a clue to battery performance.

Merkey

How do I check the Aux battery voltage?

Merkey

Replaced teh Aux battery, after charging it and main.
No joy, in fact before it would reset if I switched ignition off and on again, and now it stuck in P.

So, after a bit of research, it seems the Chinese ISM's that are available will work.

Anyone have any input on the programming side?
We had our ML fixed under the "Diesel Emissions recall" in 2022, and I believe the transmission was "Reprogrammed" to reflect the new engine ecu etc?
Does the programming need to be reinstalled or something?

Bobenis

I have this same issue with my ML350.
1st time it was a battery swap that caused it, swapping them back fixed it but this time it's either the ISM or Shift Selector.
Took the ISM out, took the cover off & it looks fine inside.
Motors all work but it keeps flipping the emergency motor to flip it into P but the spring actuator wont reset.
I too am wondering about the Chinese ones.