2020 Volvo VNL 760 - SPN 5246 FMI 0 SCR Induction Assistance / Derate

Question

Truck is stuck in a 5 MPH derate countdown. It says 'DEF Quality Low' on the dash but I just filled up with fresh BlueDEF from a high-volume pump. The code is 5246 FMI 0. My NOx sensors are only a year old.

I can't even get the truck to move to a shop. I've tried unhooking the batteries to reset the clock but it comes right back. Could this be the DEF pump or the actual injector?

ShopBossMike · Accepted Answer

✅ Confirmed fix: This was a failed DEF pump internal heater. On the D13, if the fluid doesn't reach the required temp for the SCR catalyst to work, it flags it as 'bad quality' fluid. Replaced the DEF pump module and performed an SCR crystals sublimation drive. Derate cleared after the 'DEF Service' reset in Tech Tool.

JeepJunkieJoe · Answer

Have you checked the DEF dosing valve? If it's crystallized, it won't spray. Take it out and put it in a bucket of hot water to see if the crystals dissolve, but you'll still need Tech Tool to reset the derate.

2020 Volvo VNL 760 - SPN 5246 FMI 0 SCR Induction Assistance / Derate

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