P20F3SCR NOx Pre-Catalyst Efficiency Below Threshold (Bank 2)
- 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
- P20F3 states that the SCR pre-catalyst on bank 2 no longer converts enough NOx. It belongs to engines with a separate aftertreatment line per bank and a two-stage SCR in each, with a NOx sensor between front and main brick so that the front stage can be judged on its own, an option CARB grants for catalysts arranged in series. No manufacturer documents P20F3 publicly; Hino's use of the bank 1 code P20EF is the nearest documented case. The multi-stage SCR application US20150096287 explains the logic: each stage gets its own efficiency target, and a weak front stage can be hidden because the rear stage compensates, which is why it needs its own monitor. Typical faults are a blocked front dosing valve or a heat-damaged pre-catalyst. P20F2 covers the bank 2 main catalyst. The driver usually only sees the MIL.
- What you may notice
- Malfunction indicator lamp on
- Increased NOx after cold starts
- Likely causes
- LikelyBank 2 front dosing valve blocked or crystallised
- PossibleNOx sensor between the bank 2 stages reading wrong
- PossibleBank 2 pre-catalyst damaged by heat or contamination
- 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 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.