P20EE code meaning
SCR NOx Catalyst Efficiency Below Threshold (Bank 1)
Powertrain system Generic code P20xx codes Check engine light
What P20EE means
P20EE is the main monitor CARB requires for the NOx-reducing catalyst: the share of NOx removed by the SCR catalyst on bank 1, judged by the NOx sensors before and after it, has fallen below what the system needs. Ford's 2023 6.7 L diesel fails it when cumulative efficiency drops under 55 % with the SCR inlet at 200–320 °C. GM's 2018 diesels compare measured with expected efficiency, partly via an EWMA filter, as a Type A code. Ram and Jeep 3.0 L and 6.7 L diesels had bulletins replacing the SCR catalyst (18-064-15, 18-038-16), Isuzu N-Series and the 2015 Cruze diesel got new software. Because poor DEF also cuts efficiency, GM pairs this code with a DEF quality warning, and a speed limit may follow. Check DEF quality, dosing, leaks and NOx sensors before condemning the catalyst.
P20EE at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairAfter a drive cycle
Symptoms of P20EE
- Malfunction indicator lamp on
- DEF or exhaust fluid quality warning in the instrument cluster
- Speed limitation countdown on some vehicles if the fault persists
Common causes of P20EE
- Most likelyDiluted or contaminated DEF, or a clogged or leaking dosing valve
- Most likelyUpstream or downstream NOx sensor reading wrong
- PossibleSCR catalyst aged, overheated or poisoned
- Less likelyExhaust leak between the two NOx sensors
- Less likelyCalibration needing an update (several manufacturer bulletins)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
SCR catalystNox sensor upstreamNox sensor downstream
What each part of P20EE means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| EE | The exact fault in that area. |
What to do next
- Note P20EE and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P20EE
What does P20EE mean?
P20EE means "SCR NOx Catalyst Efficiency Below Threshold (Bank 1)". P20EE is the main monitor CARB requires for the NOx-reducing catalyst: the share of NOx removed by the SCR catalyst on bank 1, judged by the NOx sensors before and after it, has fallen below what the system needs. It is a generic code, so it means the same on every make.
Is it safe to drive with P20EE?
Drive gently and only to a workshop. With P20EE the car can go into limp mode (reduced power) to protect itself.
Will P20EE fail an emissions test?
Yes, it can. P20EE is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P20EE to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P20EE clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.