Kenworth T680 PACCAR MX-13 Derate - SCR Conversion Efficiency Low

Question

I am getting a 5MPH derate warning on my 2018 T680 while hauling a full load. The dash is throwing a MIL for SCR efficiency and it will not stay in a forced regen for more than 10 minutes before failing. DEF tank is full and I don't see any white power around the injector.

Sarah Thompson · Accepted Answer

The issue was a crystallized decomposition pipe and a failed downstream NOx sensor (Part #22303391). I removed the decomp pipe and manually chipped out the urea buildup, then performed an SCR crystal sublimation drive cycle. After replacing the downstream sensor and clearing the learned data with Davie4 software, the derate cleared and the efficiency tests passed. Total cost was about $650 for the sensor and 4 hours of labor.

obd2_owl · Answer

Verify that your coolant temps are reaching at least 180F. If the thermostat is stuck open and the engine is running too cold, the SCR catalyst won't reach the light-off temperature required to process the NOx properly.

Dave Kowalski · Answer

Check your DEF quality with a refractometer first. If you got a bad batch of fluid or if there is any diesel contamination in the DEF tank, it will trigger an efficiency code immediately because the NOx conversion won't meet the expected map.

Kevin Tran · Answer

You need to pull the DEF doser and look inside the decomposition pipe. Even if the injector looks clean, the pipe itself often gets a massive buildup of crystallized DEF (the 'volcano' effect) which blocks the spray pattern and kills the conversion rate.

Kenworth T680 PACCAR MX-13 Derate - SCR Conversion Efficiency Low

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