P0420 on a 2020 Jeep Wrangler

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 2020 Jeep Wrangler

Ranked from 597 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Recurring misfires from valvetrain wear damaging the catalyst
High severity
Owners documented misfire confirmed by metal shavings in the oil and repeated camshaft/lifter/rocker-arm failures on this engine; sustained misfire dumps unburned fuel into the exhaust and can overheat/erode the catalyst.
Reported in 5 NHTSA complaints
Parts:camshaft valve lifters catalytic converter
2
Overheating-related exhaust/engine damage
Medium severity
An unwarned thermostat overheating event that cost this engine its compression can also damage nearby exhaust components and catalyst efficiency.
Reported in 1 NHTSA complaint
3
Worn or deteriorated catalytic converter
Medium severity
Normal aging reduces oxygen-storage capacity below what the rear O2 sensor needs to confirm efficiency, the most common P0420 trigger on any vehicle.
Common cause
Parts:catalytic converter
4
Failing downstream (post-catalyst) oxygen sensor
Medium severity
A slow or drifting rear O2 sensor can mimic a degraded catalyst even when the converter itself is fine.
Common cause
Parts:oxygen sensor
5
Exhaust leak between the engine and the rear oxygen sensor
Medium severity
A leak upstream of the sensor lets in outside air that skews the efficiency reading.
Common cause
6
Oil or coolant contamination of the catalyst
Medium severity
Oil or coolant burned past worn engine seals coats the catalyst substrate and poisons its ability to convert exhaust gases.
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