Paccar MX-13 Red Stop Lamp - SPN 5394 FMI 5 (SCR Dosing Defrost)

Question

Running a 2018 Kenworth T680 and just got hit with a red stop lamp and a 5 mph derate warning. The truck was fine until the temps dropped to sub-zero last night in Wyoming, now it won't let me build speed. I hooked up DAVIE4 and I am seeing an open circuit fault on the DEF dosing line heater.

Kevin Tran · Accepted Answer

The issue was a failed DEF pressure line heater (the line from the pump to the injector). I ohm'ed out the line and it was completely open. Replaced the heated line assembly, part number 2101452PE, which cost about $340 at the dealer. After clearing the codes with DAVIE and performing a forced regen/SCR system test to verify the thaw cycle, the derate cleared and hasn't returned.

shoptech_carlos · Answer

Check the resistance at the DEF line connector. You should be seeing somewhere between 2 to 5 ohms on a good heating element; if it's infinite, the internal heating wire is snapped.

Mike Reynolds · Answer

Make sure you check the harness side for 12v. Sometimes the harness rubs through right near the frame rail clip and shorts out before it even gets to the line heater connector.

road_rambler · Answer

If you are in a pinch and need to get out of the derate to reach a shop, some guys use a resistor to fool the ECU into thinking the heater is intact, but the DEF will likely freeze again if it's truly cold out.

Paccar MX-13 Red Stop Lamp - SPN 5394 FMI 5 (SCR Dosing Defrost)

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