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Trouble code
P20EE: SCR NOx catalyst efficiency below threshold
The same code points to different failures on different engines. Below, engine by engine, are the documented failures whose records name P20EE, 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)Ram 1500 EcoDiesel (2014-2019)Duramax 3.0 (LM2/LZ0)
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 →
Ram 1500 EcoDiesel (2014-2019)
1 documented failure names this code. All about this engine
verified
How widespread: Common
Where its record names the code
- 'SERVICE DEF SYSTEM - ENGINE WILL NOT RESTART IN 200 MI' warnings, DEF gauge stuck (commonly ~1/4), P20EE/P20E8 codes
Its other signs
- cold-weather faults from an inoperative tank heater; repeated tank-unit failures reported (2-3 replacements), often out of warranty
How to tell it apart
- read the DEF codes before replacing the tank - NOx-sensor and doser faults mimic the warnings
- cold-weather-only faults = heater circuit; year-round gauge faults = level/quality hardware
Usual fix
replace the DEF tank assembly (heater + level/quality hardware ride on the tank unit)
Root cause, parts and sources →
Duramax 3.0 (LM2/LZ0)
1 documented failure names this code. All about this engine
aggregated
How widespread: Occasional
Where its record names the code
- P20EE (NOx catalyst efficiency) and NOx sensor circuit codes, CEL
Its other signs
- may accompany the DEF derate ladder when SCR efficiency reads low
How to tell it apart
- confirm which sensor position is coded before ordering (GM splits position 1/2)
Usual fix
replace the coded NOx sensor (position split per GM)
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.