P0420 on a 2022 Ford F 150 Super Crew

P0420 means the downstream oxygen sensor pattern suggests the bank 1 catalytic converter is not storing oxygen properly.

Not your vehicle? See general P0420 info.

Most common causes on the 2022 Ford F 150 Super Crew

Ranked from 559 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Catalyst damage from prior cylinder misfires (2.7L EcoBoost intake-valve failures)
High severity
Several owners in this batch document an intake-valve failure with an explicit misfire warning and rough/near-stalling idle beforehand; unburned fuel reaching the converter from sustained misfires overheats and melts the catalyst substrate.
Reported in 4 NHTSA complaints
Parts:catalytic converter
2
Exhaust/gasket leak at or near the catalytic converter
Medium severity
An owner reports exhaust fumes and headaches from a leak traced to the catalytic converter/exhaust gasket area, which both damages sensor accuracy and can reduce effective conversion efficiency.
Reported in 1 NHTSA complaint
Parts:exhaust gasket
3
Worn or aged catalytic converter
Medium severity
Normal thermal aging of the catalyst substrate over time and mileage eventually drops conversion efficiency below the monitored threshold.
Common cause
Parts:catalytic converter
4
Failing downstream O2 sensor
Low severity
A degraded rear sensor can mimic a catalyst-efficiency fault even when the converter itself is still good.
Common cause
Parts:oxygen sensor
5
Oil contamination of the catalytic converter
Medium severity
Oil reaching the exhaust from internal engine wear coats and poisons the catalyst's active surface.
Common cause
Parts:catalytic converter
6
Coolant contamination of the catalytic converter (head gasket leak)
Medium severity
Coolant burned through a leaking head gasket disables the catalyst and is a less common but recognized cause of P0420.
Common cause
Parts:catalytic converter head gasket

Part links go to Amazon search results for this vehicle. As an Amazon Associate, WrenchConnect earns from qualifying purchases — always confirm fitment for your exact trim and engine before ordering.

These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0420 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Usually no drivability issue
Failed emissions test
Sulfur smell in some cases
Reduced power if converter is clogged

What to check before replacing parts

Check for misfire and fuel trim codes first

Look for: Any active or recent misfire, or lean/rich trim codes, means raw fuel or an off mixture has likely already damaged or is currently overworking the converter — fix those before touching the catalyst.

Inspect for exhaust leaks ahead of the converter

Look for: A leak before the converter (cracked manifold, loose flange, blown gasket) lets in outside air that confuses the downstream O2 sensor into reading as if the catalyst isn't working, even when it is.

Compare upstream and downstream O2 sensor activity

Look for: A healthy converter makes the downstream sensor read flat and steady while the upstream sensor swings actively. If the downstream sensor switches nearly as fast as the upstream one, the converter isn't storing oxygen properly and is likely worn out.

Check converter temperature and performance

Look for: A converter outlet noticeably cooler than expected relative to its inlet under load suggests little catalytic reaction is happening inside — supports a genuinely failed converter rather than a false reading.

Hold off on replacing the converter until root causes are ruled out

Look for: If misfires, exhaust leaks, or fuel trim issues caused this code, a new converter will fail again quickly — confirm those are clean first.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Check Engine Light