P20EESCR NOx Catalyst Efficiency Below Threshold (Bank 1)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Malfunction indicator lamp on
- DEF or exhaust fluid quality warning in the instrument cluster
- Speed limitation countdown on some vehicles if the fault persists
- Likely causes
- LikelyDiluted or contaminated DEF, or a clogged or leaking dosing valve
- LikelyUpstream or downstream NOx sensor reading wrong
- PossibleSCR catalyst aged, overheated or poisoned
- RareExhaust leak between the two NOx sensors
- RareCalibration needing an update (several manufacturer bulletins)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €4,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.