2016 GU533 w/ Allison & ISL9. I have all the codes here, save for the 3232 intake NoX. And also have the 6656. 6656 2771 3714 4152 4151 4677 4572 I've been handed this from the other techs, and they say that they have 12.3 volt (and verified ground) at all of the components listed above. Battery shows 12.4. Leaving them unplugged, one at a time, and, using INSITE, the codes never change. They put in a new DEF header, no change. How do I test the CAN for issues? And, I've never used INSITE, so that's Greek to me, too.
you can start with verifying termination resistors (should be 120ohm) and continuity in can wires, you really need an oscilloscope to dive deep in can issues. snap on has a decent guide for how can works https://www.snapon.com/EN/US/Diagnostics/News-Center/CAN-Bus Quick Tip: CAN Bus Diagnostics im guessing it probably need an Aftertreatment Control Module
Where is the aftertreatment control module located? What does it look like?
i was thinking mp8 for some reason, the cummins manages aftertreatment through the ecm, sorry for that, i would verify everything(termination resistors,wire continuity/resistance,etc..) before condemning the ecm
First make sure you have 12 volts to the aftertreatment sensors. I like to test it with a light bulb even if the meter says there is 12 volts. The data link wires, measure resistance between them with the key turned off, should be close to 60 ohms. I don't recall where the terminating resistor is at the aftertreatment module. It may be in one of the sensor modules, if you unplug the module with the terminating resistor the meter will read 120 ohms. The terminating resistor at the front of the data link is inside the turbo actuator. Then with the key on measure the voltage at each wire to a good ground. You should have close to 2.5 volts with one being slightly higher than the other. Broken wires near the aftertreatment assy are common.