P0420 on a 2019 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 2019 Honda Cr V

Ranked from 1,063 NHTSA owner complaints filed for this vehicle.

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1
Head-gasket failure letting coolant/oil into the exhaust, contaminating the catalytic converter
High severity
Nine of the thirty retrieved complaints on this 2019 CR-V describe a blown/leaking head gasket (a well-documented issue on the 1.5L turbo engine); coolant/oil intrusion into the cylinders washes through and poisons the catalyst.
Reported in 9 NHTSA complaints
Parts:head gasket catalytic converter
2
Catalyst overheating from chronic multi-cylinder misfire
High severity
Several complaints document P0301-P0303 misfires traced to failing fuel injectors; sustained misfire overheats and melts the substrate.
Reported in 3 NHTSA complaints
Parts:fuel injector ignition coil spark plug
3
Extended rich-running from the 1.5T oil-dilution/injector defect
Medium severity
Owners report an oil-dilution condition with fuel injectors running the mixture rich, a widely documented issue on this engine that accelerates catalyst wear.
Reported in 2 NHTSA complaints
Parts:fuel injector
4
Excessive oil consumption from worn piston rings contaminating the catalyst
Medium severity
One complaint describes suspected collapsing/sticking piston rings causing severe, unmeasured oil consumption; oil burned through the cylinders coats and poisons the catalyst.
Reported in 1 NHTSA complaint
5
Worn or aged catalytic converter
Medium severity
Baseline wear-and-age cause common to all vehicles at sufficient mileage.
Common cause
Parts:catalytic converter
6
Failing downstream (post-catalyst) O2 sensor
Medium severity
A lazy or degraded rear sensor can read like a genuine efficiency drop.
Common cause
Parts:oxygen sensor
7
Exhaust leak upstream of the downstream O2 sensor
Medium severity
A leaking manifold gasket or cracked pipe ahead of the rear sensor skews the reading.
Common cause
Parts:exhaust gasket
8
Aftermarket or damaged exhaust component
Low severity
A non-OEM converter or collapsed pipe section rarely meets the OEM efficiency threshold.
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.

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

Matching symptoms

Check Engine Light