Failure mode - Cummins 6.7L ISB Diesel (Ram HD)

DEF / SCR system failures (2013-2018)

Reliability tier: verified - verify before ordering, see /disclosure/

Symptoms

DEF-system warning / 'service DEF system' message, then 5 mph derate if ignored
NOx sensor DTCs (P2200-family); 'DEF quality poor' messages
DEF pump / heater failure, especially after a freeze (pump assembly contains a heater)
white crystalline urea deposits around the DEF tank, pump and injector
failed emissions test / MIL with no driveability change

Compare with the other causes of the same sign on this engine: loss of power, limp mode or derate (6 causes) · def, dpf and regeneration warnings (4 causes)

Root cause

The 2013+ SCR system adds a consumable-fluid path (DEF tank, pump with heating element, dosing injector, NOx sensors, SCR catalyst). Failures concentrate in the pump/heater assembly (freeze damage), contaminated or old DEF, and NOx sensor electronics. Contamination crystallizes in lines and the injector.

Diagnosis

read DEF/SCR DTCs and current DEF quality / NOx PIDs before parts-cannoning
inspect DEF for contamination/crystals; sample age - DEF has a shelf life and degrades with heat
verify tank heater and pump operation on a cold morning (freeze-related no-starts of the dosing system)
check dosing injector for crystallization; verify NOx sensor readings upstream/downstream of SCR make physical sense

Fixes

drain and flush contaminated DEF; fresh DEF (dated stock, stored cool); clear crystals from the injector ()

DEF Fluid (2.5gal case, dated stock)

replace the failed component - DEF pump assembly (with heater), NOx sensor, or dosing injector - per DTC ()

Prevalence

common