2018 Freightliner Cascadia DD15 SPN 3216 FMI 20 - SCR Efficiency Low Derate

Question

My truck just went into a 5 mph derate after showing an SCR efficiency code. I am hauling a heavy load and need to get back on the road, but the dash says SCR Service Required and won't let me clear it with my basic scanner. It seems like it's consuming more DEF than usual lately.

Mike Reynolds · Accepted Answer

The issue was a failed DEF doser injector (Part #A0001401539) that was leaking internally and a contaminated DEF pump filter. I replaced the doser valve, cleaned the decomposition pipe which was full of urea crystals, and performed a forced SCR efficiency reset using Diagnostic Link 8.15. The truck required a full 45-minute parked regen followed by the efficiency test to clear the 5mph derate. Total parts cost was around $450 plus 3 hours of labor.

Carlos Diaz · Answer

You need to perform a 'SCR Efficiency Test' using Detroit Diagnostic Link. Just replacing sensors doesn't reset the monitors for the EPA13/GHG17 platforms.

Tom Patel · Answer

Check your DEF doser valve nozzle. If it is crystallized or leaking, you won't get the correct atomization, which triggers the efficiency code even if the sensors are new.

Dave Kowalski · Answer

Since you mentioned high DEF usage, check the coolant lines going to the DEF tank. Sometimes the internal heating element cracks and leaks coolant into the DEF, which ruins the SCR catalyst.

2018 Freightliner Cascadia DD15 SPN 3216 FMI 20 - SCR Efficiency Low Derate

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