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Trouble code
P204F: reductant (DEF) system performance
The same code points to different failures on different engines. Below, engine by engine, are the documented failures whose records name P204F, with the record's own words, how to tell them apart and the usual fix. The meaning above is taken from the record DEF / SCR / NOx sensor faults.
6.7 Power Stroke (2011-present)6.7 Cummins 2007-2018
6.7 Power Stroke (2011-present)
1 documented failure names this code. All about this engine
verified
How widespread: Very common
112 NHTSA owner complaints match it, out of 1,754 checked
Where its record names the code
- check-engine light with codes P20EE (SCR efficiency below threshold), P2200-series (NOx sensor circuit/performance), P204F (reductant/DEF system performance)
Its other signs
- progressive derate warnings culminating in a 5mph limp if unaddressed
- DEF warnings/low-dose faults that persist even with a freshly filled, good-quality tank
How to tell it apart
- verify actual dosing BEFORE replacing any sensor: test DEF concentration with a refractometer, inspect the DEF injector tip for crystal buildup, confirm commanded dosing with a scan tool, check for exhaust leaks upstream of the sensors
- NOx sensors are not cheap - do not condemn one without first ruling out the injector/DEF-quality/leak alternatives above
Usual fix
replace a confirmed-failed NOx sensor (upstream or downstream of the SCR catalyst) only after verifying dosing
Root cause, parts and sources →
6.7 Cummins 2007-2018
1 documented failure names this code. All about this engine
verified
How widespread: Very common
55 NHTSA owner complaints match it, out of 1,355 checked
Where its record names the code
- read DTCs (P242F/P2463 soot-load, P204F etc.) and soot-load / ash-load PIDs before replacing anything
Its other signs
- 'exhaust filter full / regeneration required' message on the overhead console
- frequent or endless regenerations; aborted regens on short trips
- loss of power (inducement / derate) until regeneration completes
- excessive idle, white/grey smoke during regen, hot exhaust smell
- fuel smell in the oil after repeated failed regens
How to tell it apart
- read DTCs (P242F/P2463 soot-load, P204F etc.) and soot-load / ash-load PIDs before replacing anything
- verify regen completes when driven at highway load (30+ min); a filter that regens clean is a duty-cycle problem, not a part problem
- differential-pressure check across the DPF; inspect for cracked/missing substrate
Usual fix
restore duty cycle: sustained highway load so regens complete; correct the underlying reason regens fail (VGT, sensors, EGR) before replacing the filter
Recalls and bulletins
TSB 18-002-14 REV. BTSB 18-002-14 REV. ATSB 18-002-14
Root cause, parts and sources →
A code tells you which system flagged a fault, not which part failed. Read it with the signs your truck shows: symptoms by engine. For your exact truck: check your VIN.