CM870 ECM communication

[Johnh62]

Good afternoon. I have a CM870 that I'm having trouble with. The customer had a custom file in this one and we couldn't communicate with the OEM side datalink, but could connect thru the 3 pin weatherpack connector on the Cummins side of the ECM.

We bought a reman ECM pre-programmed and installed it this morning. It communicated normally thru the cab diagnostic port and ran normally except an active egr valve fault. Anyway I had our "expert" flash it to help out with that egr fault and he mentioned it failed almost thru flashing and now it won't communicate thru the OEM port again, but will communicate through the Cummins side weather pack plug. I feel like this communication issue was caused both by the previous flash and the one we just did this morning. Any ideas on how to get through this?

Thanks everyone for the help!

[marek4792]

What adapter are you using? Stop and get ahold of someone from here before you get the ECM into a "Rom Boot" state...

[Johnh62]

We are using a nexiq usb link 2 adapter. As it sits now it will not communicate on the oem side(in-cab J1708), but will communicate normally on the engine wire harness weather pack connector.

[tree98]

So is there a problem with that ?

[marek4792]

Start simple and if it isnt a counterfeit, uninstall and reinstall the drivers for it.

[Rawze]

(09-12-2025 )Johnh62 Wrote:  ...Anyway I had our "expert" flash it to help out with that egr fault and he mentioned it failed almost thru flashing and now it won't communicate thru the OEM port again, \
...

- Your first post sounds more to me like someone not knowing what the heck they are doing, more-so than anything else.

CM870's are very different than more modern ECM's. trying to copy the program from one ecm to another.. heck .. trying to copy ANY program into it that is NOT a blank Incal file itself.. will make it to things like not communicate with the dash, and other quirky/screwy things. Even trying to edit a factory incal file (with the wrong version of CT) will corrupt it enough to make it act up. - It is well known about them.


Stop trying to put bad delete files into it and put it back to its original factory programming via Insite with the file that belongs to that engine ser#. After that, restore the work order/template in Insite so that it has all the dash settings etc.

If it still does not work correctly, then chock it up to the fact that some complete idiot purchased a NON-
OEM, USED ECM!!!. - and go get a new OEM ecm instead, and have the dealership pre-flash it completely with the programming it needs to run the truck and engine (according to the engine ser# and vin#).