OBDII can be powered on, but can not communicated to ECU

Hello,

The fuse box is attached to the AAM module, the AAM module is responsible for communication, most likely there might be water or corrosion in the AA. Take it apart and check for water and or corrosion, if none found you will need to check continuity from the OBD port to the AAM and then possible replace the AAM.
Lou

Can we check for power at fuse # 22 and #13. Here is guide to help you and the ALDL connector wiring diagrams so you can see how the system works:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check out the diagrams (below). Please let us know what you find.

Cheers, Ken

Did you test #47 with the lights on? Has nothing to do with the non communication. What about fuses # 22 and #13?

Yes, it does sounds like a bad connection to the ALDL connector. Here is a guide to help you run some test use the wiring diagrams above:

https://www.2carpros.com/articles/how-to-check-wiring

Please run down this guide and report back.

Peter, what kind of scan tool are you using?

On our OBD port the AAM handles most of the communication but if you are using a generic scan tool you are only accessing the engine module and the engine module can be the issue.
You need a Mercedes capable scan tool such as the icarsoft or startool found at www. Mbstartool. Com
or a high end Snap on or Matco.
With Mercedes there is no such easy task as no communication.
Having power at the OBD port is just a fraction of the things that need to be present.
The wiring diagrams for the ML also changed every year so I would need the build date to get you the correct diagram for the car.
Also the diagrams are not easy to read if you are not familiar with them.
Here attached is the one for the 2000 built between 11/99 and 9/00.
Hope this helps.
It might be best to take this in, based on your replies you are shooting in the dark with your testing and it might be best. It can save you time and money having someone with Mercedes knowledge assist with this.
Lou

It looks like the monitors are not ready, so is this the problem? Have you had the codes cleared? Does a scanner read the computer?

Here is a guide:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Let us know, Ken

That looks like an EVAP system control solenoid. Remove the unit it should have a part number on it. Nice work fixing the communication problem.

Yes I would replace the purge solenoid and then clear the codes. Here is the location below.

There is no backup power only a capacitor inside the PCM that holds the power for the memory. I have never seen one go out but you never know. I would try a used/rebuilt PCM.
Check out the diagrams (Below). Please let us know what happens.

This is for the presets of the car has nothing to do with the computer. Did you replace the EVAP valve and clear the codes?

Okay, let me know.