P0420 on a 2017 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 2017 Nissan Rogue

Ranked from 591 NHTSA owner complaints filed for this vehicle.

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1
Failing downstream (rear) O2 / air-fuel ratio sensor
Medium severity
A lazy or contaminated downstream sensor reads similarly to the upstream sensor, mimicking a catalyst efficiency fault even with a good converter. This vehicle has an independent-shop diagnosis pointing at O2/air-fuel-ratio sensor and exhaust manifold failure.
Reported in 1 NHTSA complaint
Parts:oxygen sensor air-fuel ratio sensor
2
Exhaust leak ahead of the downstream O2 sensor
Medium severity
A leaking exhaust manifold, gasket, or pipe joint upstream of the rear sensor draws in outside air, skewing the sensor's oxygen reading and falsely indicating low catalyst efficiency; consistent with the exhaust-manifold failure diagnosis reported on this vehicle.
Reported in 1 NHTSA complaint
Parts:exhaust manifold gasket exhaust manifold
3
Worn/failing catalytic converter
High severity
The catalyst's precious-metal substrate loses oxygen-storage capacity with age/mileage, causing pre- and post-cat O2 readings to converge and tripping the efficiency monitor. Confirm with a scan tool O2 sensor switching/waveform comparison.
Common cause
Parts:catalytic converter
4
Chronic engine misfire overheating/damaging the catalyst
High severity
Unburned fuel from a persistent misfire (worn plugs/coils) ignites in the converter, overheating and melting the substrate. Check misfire counters and spark components before condemning the cat.
Common cause
Parts:ignition coil spark plug
5
Oil or coolant contamination of the catalyst
High severity
Oil burned past worn valve seals/rings or coolant from a leaking head gasket coats the catalyst's substrate and poisons its efficiency. Check oil consumption and coolant level trends.
Common cause
6
Upstream (front) O2/air-fuel ratio sensor fault causing incorrect fuel trim
Medium severity
An inaccurate front sensor lets the engine run rich or lean, which itself degrades measured catalyst efficiency even with a healthy converter. Check long-term fuel trims.
Common cause
Parts:air-fuel ratio sensor
7
Fuel delivery issue causing rich/lean running (dirty injectors, weak fuel pressure, dirty MAF)
Medium severity
An improper air-fuel mixture overworks or starves the catalyst, lowering measured efficiency. Check fuel trims and MAF/injector performance.
Common cause
Parts:fuel injector mass airflow sensor
8
Aftermarket or incorrect-spec exhaust/converter installed
Low severity
A non-OEM or high-flow converter often lacks adequate catalyst volume/coating to pass the efficiency monitor. Verify the converter is OEM-spec.
Common cause
Parts:catalytic converter

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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