Why does my John Deere 544K have DEF and NOx sensor faults?

[Nicholas Villa]

My John Deere 544K has 2,235 hours and was used on a salt project. After fixing corroded plugs, I now have DEF tank header and NOx sensor communication codes. Could corrosion or wiring be the problem?

 

[morgan65ry]

that sounds frustrating. i'd start by checking the def quality and sensor wiring before assuming both sensors have failed. what fault codes are you seeing, and is the machine still running noramlly?

 

[zernish308]

I’d start with the wiring and CAN communication before throwing parts at it. If you’re getting both the DEF header and inlet/outlet NOx communication faults at the same time, it seems like there could be a common wiring or connector issue. Has anyone found a particular harness or connector on the 544K that tends to cause these faults?

 

[johnhumphrey]

Since the machine was used on a salt project, wire corrosion is definitely the primary suspect. I'd check the harness pins for any green corrosion and inspect the ground points near the SCR unit, because a bad ground alone can easily throw off both DEF and NOx communication codes at the same time.