P20EE — SCR NOx Catalyst Efficiency Below Threshold (Bank 1) — 6.7 Powerstroke
Diagnostic reference for 6.7 Powerstroke (2011–present) P20EE.
What it means
The PCM has determined that the SCR catalyst is not reducing NOx as much as required.1
Most likely causes
- DEF quality or dosing delivery issue — Check DEF quality, the DEF doser and lines. Unresolved, Ford’s DEF warnings count down to a speed limit.1
- Contaminated or worn SCR catalyst — A contaminated or worn SCR catalyst can cause it.1
- NOx sensor reading or performance problem — Check NOx sensor readings and exhaust leaks; NOx sensor failures are common on the 6.7L Power Stroke. Check the sensor’s connector, wiring and module, and for exhaust leaks near it.12
- Reductant pressure too low — DEF (reductant) delivery pressure is below target; typical causes include DEF pump, frozen or clogged DEF line/filter, or the dosing valve.3
- Reductant system performance issue — The selective catalytic reduction (DEF) system is not achieving expected NOx reduction; typical causes include DEF quality, dosing injector, DEF pump, or NOx sensor.4
How to diagnose
- Verify freeze frame and confirm P20EE is active with matching NOx sensor data.
- Inspect DEF quality and level; verify correct specification and no contamination.
- Check for DEF dosing system faults: reductant pressure, pump operation, lines/filters for freeze/clog, and dosing valve function.
- Inspect exhaust for leaks upstream of the NOx sensors and around sensor bungs.
- Review NOx sensor data: compare upstream (Bank 1 Sensor 1) and downstream readings for expected conversion; check sensor connector, wiring and module condition.
- If no dosing or sensor faults are found, evaluate SCR catalyst condition for contamination or wear.
- Clear codes, perform a drive cycle under conditions that enable SCR monitoring, and re-check for P20EE return.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| DEF urea concentration | 32.5% (check with a DEF refractometer) | Sample from the tank | Ram service bulletin 25-005-14 (Diesel Exhaust Fluid) |
| DEF freeze point | About 12°F (−11°C); freezing alone is normal and the system is built to thaw it | Cold weather | Ram service bulletin 25-005-14 (Diesel Exhaust Fluid) |
Common mistake to avoid
Replacing sensors, the doser or the SCR catalyst before testing the DEF. Old, heat-stored or diluted DEF loses strength and sets the same efficiency codes. Check it with a refractometer first. Source: Ram service bulletin 25-005-14 (Diesel Exhaust Fluid).
Parts and tools you may need
- OBD-II scan tool with live data
- NOx sensor test harness/connector inspection kit
- DEF refractometer or test strips
- Exhaust leak detection spray or smoke machine
Tools you’ll need
- OBD-II scan tool — Reads P20EE freeze frame and live NOx sensor data to confirm SCR efficiency and monitor reductant system parameters.
- digital multimeter — Checks NOx sensor heater and signal circuits for proper voltage and resistance to rule out sensor or wiring faults.
- refractometer — Verifies DEF concentration is within specification to eliminate poor-quality reductant as the cause of low SCR conversion.
- pressure gauge — Measures reductant pump/line pressure to confirm dosing system can deliver DEF at required pressure for proper injection.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| DEF injector (doser) | $200–$600 | 0.5–2 hrs | DIY with tools and a manual |
| NOx sensor | $250–$800 | 0.5–2 hrs | DIY with tools and a manual |
| DEF pump / supply module | $400–$1,200 | 1–3 hrs | DIY with tools and a manual |
| SCR catalyst | $2,000–$4,500 | 1–4 hrs | Shop |
Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.
When to see a pro
High-pressure fuel and exhaust aftertreatment work can be hazardous. If you are not trained on diesel aftertreatment diagnostics, have a qualified diesel technician perform testing and repairs.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
Repair videos: P20EE on the 6.7 Power Stroke
Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.
Spotted an error, or something missing? Tell us
Run a 6.7 Powerstroke? This goes straight to the editor — it is not published.