Paccar MX-13 Red Stop Lamp - SPN 5246 FMI 0 SCR Derate

Question

My 2018 T680 is stuck in a 5 mph derate and I cannot get the parked regen to start even with the dash switch. The DEF tank is full but the gauge is flickering and I'm seeing multiple SCR performance codes. I need to get this moving ASAP as I have a load of produce sitting in the trailer.

Kevin Tran · Accepted Answer

The issue was a failed DEF Quality Sensor header assembly inside the tank and a skewed Outlet NOx sensor. Replaced the DEF tank header (Part #2104868PE) and the Outlet NOx sensor (Part #2296798). After clearing the codes and performing a 'Deep Forced Regen' via DAVIE 4, the derate cleared and the SCR efficiency returned to 98%. Total parts cost was around $1,100 plus 4 hours of labor.

Jordan Lee · Answer

Verify the DEF quality using a refractometer. If the fluid has shifted from the 32.5% concentration, or if there is diesel contamination in the DEF tank, the SCR efficiency will drop and force a derate.

backyard_bart · Answer

Check the DEF pump filter located at the bottom of the supply module. If that filter is clogged with crystallized urea, you won't get enough pressure to the injector for a successful regen, which triggers that 5246 code.

Tom Patel · Answer

You need to check your NOx sensor values using DAVIE software. If the inlet and outlet sensors aren't crossing a specific threshold during the heat-up cycle, the ECM will block any manual regen attempts to protect the DPF.

Paccar MX-13 Red Stop Lamp - SPN 5246 FMI 0 SCR Derate

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