P0420 on a 2016 Honda Cr V

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 2016 Honda Cr V

Ranked from 388 NHTSA owner complaints filed for this vehicle.

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1
Chronic oil consumption contaminating the catalyst
High severity
This CR-V generation is well known for burning oil from worn/stuck piston rings; the resulting ash and oil vapor coat and poison the catalyst media over time.
Reported in 6 NHTSA complaints
2
Worn or degraded catalytic converter
High severity
One owner had the catalytic converter itself replaced after the check-engine light cycled on an emissions/catalyst code.
Reported in 1 NHTSA complaint
Parts:catalytic converter
3
Failing downstream O2 sensor
Medium severity
The same owner who replaced the converter found the recurring code linked to O2 sensor involvement in follow-up research.
Reported in 1 NHTSA complaint
Parts:oxygen sensor
4
Failing MAF sensor skewing fuel trim
Medium severity
A drifting MAF sensor was implicated alongside the O2 sensor in this owner's research into the recurring catalyst code.
Reported in 1 NHTSA complaint
Parts:mass airflow sensor
5
Prior or ongoing misfire overheating the converter
High severity
An owner who replaced the fuel pump, injectors, plugs, and an ignition coil for persistent rough running/stalling shows a misfire history that can overheat and damage a catalyst.
Reported in 1 NHTSA complaint
6
Exhaust leak upstream of the sensor
Low severity
A leak ahead of the catalyst lets in outside air and mimics reduced conversion efficiency; check manifold gaskets and joints.
Common cause

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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.

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Matching symptoms

Check Engine Light