Trouble codes › P20EE

P20EE SCR NOx Catalyst Efficiency Below Threshold (Bank 1)

Diesel emissions

P20EE means the diesel SCR (DEF) system isn't cutting NOx enough, often from bad DEF, a NOx sensor or software needing an update.

On diesels with DEF (diesel exhaust fluid), the SCR catalyst uses DEF to clean NOx from the exhaust. P20EE means NOx levels after the catalyst are too high, so it isn't working well enough.

Can I keep driving? Yes, but get it fixed soon.

Drivable, but many trucks count down to a speed limit (often 5 mph) if it isn't fixed. Get it checked soon.

Common causes

  1. Poor-quality, old or contaminated DEF
  2. A clogged or failing DEF injector or pump
  3. A failing NOx sensor
  4. A worn SCR catalyst
  5. Software that needs an update (common fix)

Symptoms

  • Check-engine light and DEF or emissions warnings
  • A countdown to reduced speed
  • Higher DEF use or deposits around the DEF injector

What to check first

  1. Check DEF quality (a refractometer or test strips) and replace old DEF.
  2. Look for crystal deposits at the DEF injector.
  3. Check for service bulletins and software updates: many trucks have them for P20EE.
  4. Have NOx sensor readings and DEF dosing tested with a scan tool.

What does P20EE mean on your vehicle?

The likely cause depends on your engine. iRepair researches your exact year, make, model and engine (service bulletins, recalls and owner reports) and tells you what to check first. Your first 3 questions are free.

Ask iRepair about P20EE

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Related codes

General guidance for P20EE on most vehicles. Some makers use the same code a little differently; confirm in the service information for your vehicle, put safety first, and see a professional when in doubt.