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

Ken,
Thank you,

I rechecked all of fuse with key in 2, did as your link, all fuse are good, only F47 there is no power.
I am going to check headlamp housing, if the fog sockets have bad connection.
Anything else I should check over?

Peter

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

Hi, Ken,

All fuses are good, voltmeter made beep sounds at both ends of each fuse, including 22 and 13, except #47 (front fog lamp). I turned the switch rod to the fog position no lights on, I believe it should be yellow lights. So, I think maybe there is a bad connection? What do you think?

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

I should first post the smoke check report. So, can know what I am talk about and what should I do about it. See the picture.

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

Hi, Ken,
OBD II can be powered on.
Check engine light can be on with all other lights when key in position 2.
There no codes showed. (Visual Inspection PASS ?)
"There no communication to ECU ",
(see picture from OBD II Ancel AD410, as well as from O'Reilly Auto Parts's OBD II Botch.)
Thanks

Peter

Hi, All,
Is the communication successful? I did not see my OBD II show the lines before.
If it is, that means I fond it !
The wire is bad.
What is the part's name?
See two pictures,

Thanks all.

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.

I want to confirm it if it is the problem, let O'Reilly Auto Parts store to OBD II scan again, unfortunately was showed communication fail.

And I checked it at home with key in position 2,
OBD II show the DTC again :
Review DTC >
Pending DTC's ($07) >
P0443 EVAP System Purge Control Valve A Circuit

Hi, Ken,
Should I replace the EVAP Purge Solenoid Control Valve ?

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

Hi, Ken,

I did not replace anything, send it to the dealer want to get a high end test. Later the day I got called, said found nothing, technician next will make the long drive for computer self-reset.

So far, the cost I know already reached at $390.00.
According this kind of situation, I am wondering that vehicle computing needs a backup battery that would save a lot of time, and money, and suffers.

Hi, Ken, do you know anything about the vehicle computer backup power?

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.

Hi, Ken,

Is there a solution to prevent vehicle computer data lost?
https://www.powerstream.com/DC-UPS-1212.htm

Peter

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?

I did not replace EVAP valve and anything.
I sent it to the dealer. The dealer had found nothing either.
Today will call me for the result about their long drive for computer self-resetting.

Okay, let me know.