P20F3 code meaning
SCR NOx Pre-Catalyst Efficiency Below Threshold (Bank 2)
Powertrain system Generic code P20xx codes Check engine light
What P20F3 means
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.
P20F3 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 P20F3
- Malfunction indicator lamp on
- Increased NOx after cold starts
Common causes of P20F3
- Most 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
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
SCR pre catalystNox sensor
What each part of P20F3 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. |
| F3 | The exact fault in that area. |
What to do next
- Note P20F3 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 P20F3
What does P20F3 mean?
P20F3 means "SCR NOx Pre-Catalyst Efficiency Below Threshold (Bank 2)". P20F3 states that the SCR pre-catalyst on bank 2 no longer converts enough NOx. It is a generic code, so it means the same on every make.
Is it safe to drive with P20F3?
Drive gently and only to a workshop. With P20F3 the car can go into limp mode (reduced power) to protect itself.
Will P20F3 fail an emissions test?
Yes, it can. P20F3 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 P20F3 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P20F3 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.