P0420 on a 2018 Nissan Rogue

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 2018 Nissan Rogue

Ranked from 609 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Oil consumption contaminating the catalyst
Medium severity
The oil-burning/leak pattern reported on this engine can coat the catalyst in ash over time and reduce its efficiency.
Reported in 2 NHTSA complaints
Parts:catalytic converter
2
Coolant or combustion-gas intrusion from a cracked block
High severity
One owner's cracked engine block (recall NTB20-25A) can send coolant into the exhaust stream, damaging catalyst efficiency.
Reported in 1 NHTSA complaint
3
Worn or degraded catalytic converter
Medium severity
Normal high-mileage aging reduces the catalyst's oxygen-storage capacity below the efficiency threshold the ECM monitors.
Common cause
Parts:catalytic converter
4
Failing downstream (post-catalyst) oxygen sensor
Low severity
A lazy or biased rear sensor can mimic reduced catalyst efficiency even when the catalyst itself is fine.
Common cause
Parts:oxygen sensor
5
Exhaust leak ahead of the downstream sensor
Low severity
A leaking joint or gasket ahead of the sensor lets in outside air, skewing the efficiency comparison.
Common cause
6
Long-term misfire damaging the catalyst substrate
Medium severity
Unburned fuel from an uncorrected misfire overheats and degrades the catalyst's internal structure.
Common cause

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