2019 Volvo VNL 760 - SPN 5394 FMI 5 - DEF Dosing Malfunction

Question

Got an SCR performance code and now the truck is in a soft derate. The DEF gauge shows half full, but the computer thinks the system isn't dosing correctly. I checked the DEF pump filter and it was a bit dirty but not blocked.

I'm worried the SCR brick is dead. I've been running cheap DEF from a local warehouse and I'm wondering if I got a bad batch or if the pump itself is giving up.

FreightlinerFred · Answer

✅ Confirmed fix: The DEF doser valve had an open circuit internally (FMI 5 usually indicates low current/open circuit). After replacing the injector/doser valve and performing a 'Crystal Sublimation' drive cycle, the code cleared and stayed off.

SuspSpecSal · Answer

You need to run a DEF quantity test using Premium Tech Tool (PTT). It's possible the pump is failing to build the required 9 bar of pressure, even if the electrical side looks okay.

2019 Volvo VNL 760 - SPN 5394 FMI 5 - DEF Dosing Malfunction

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