Paccar MX-13 Aftertreatment Derate - 5 MPH limit active

Question

My 2018 Peterbilt 579 is stuck in a severe derate and I have a 5 MPH limit warning on the dash. I was climbing a grade when the MIL came on and now I can't get any power even on flat ground. Both DEF tank levels look fine but it won't let me perform a parked regen.

dieselmike88 · Accepted Answer

The issue was a completely failed DEF Dosing Valve (Part #2115825). I pulled the injector and it was heavily crystallized. After replacing the valve and the supply line gasket, I had to use DAVIE4 software to perform a 'Force SCR Reset' and a 'Service Regen' to clear the inducement code. Total parts cost was $485 and the truck is pulling hard again with no codes.

torque_terry · Answer

You need to check your DEF doser valve. If it's crystallized or plugged up, the system can't inject fluid to lower NOx levels, which will trigger that 5 MPH derate quickly on EPA17 engines.

garagegrease · Answer

Have you looked at the DEF pump pressure? If the internal filter is clogged or the pump diaphragm is shot, you won't get the 130 PSI needed for the dosing cycle to complete.

Pete Sanders · Answer

Check the outlet NOx sensor. Those Paccar units are notorious for failing around 400k miles. If the sensor is reading static or out of range, the SCR efficiency test fails and puts you in an inducement state.

Paccar MX-13 Aftertreatment Derate - 5 MPH limit active

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