Powertrain, generic (extended)

P20EF SCR NOx Pre-Catalyst Efficiency Below Threshold (Bank 1)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P20EF concerns the front stage of an SCR arrangement with two stages on bank 1: the pre-catalyst no longer removes enough NOx. CARB allows catalysts in series to be monitored individually or together; this code is used where the front stage is checked separately, which requires a NOx sensor between the two bricks. Paccar's patent US11976582 describes such a layout and computes the front stage's efficiency from NOx entering and leaving it. Hino uses P20EF on 2016–2019 trucks with J08E and J05E engines; bulletin SB-18-024 corrected the workshop troubleshooting for it, without public thresholds. A failing front stage shifts load to the main catalyst, so overall NOx may still look acceptable at first. P20EE covers the main catalyst, P20ED overheating of the pre-catalyst. The driver mainly sees the MIL.

Likely causes

Front DEF dosing valve clogged, crystallised or leaking
NOx sensor before or between the stages reading wrong
Pre-catalyst thermally aged or poisoned
Poor DEF quality

Symptoms

  • Malfunction indicator lamp on
  • Higher NOx at low exhaust temperatures, for example after cold starts

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–3,000
Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

scr pre catalystnox sensor

Related codes

P20EEP20EDP20F3P2200P2201

References: static.nhtsa.gov, patents.google.com, law.cornell.edu.