P0420 on a 2019 Jeep Cherokee

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 Jeep Cherokee

Ranked from 1,596 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Catalyst damage from unresolved cylinder misfires (2.0L turbo internal wear)
High severity
This vehicle has documented misfire complaints (including one flagged as a severe misfire right after a dealer visit) alongside low-compression and catastrophic engine-failure reports; raw fuel from ongoing misfires can overheat and melt the catalyst substrate.
Reported in 2 NHTSA complaints
Parts:catalytic converter
2
Oil contamination of the catalyst from internal engine wear
Medium severity
One owner reported ongoing oil consumption with the check-engine light on and no other stored codes, consistent with oil ash slowly coating and poisoning the catalyst.
Reported in 1 NHTSA complaint
Parts:catalytic converter
3
Worn or aged catalytic converter
Medium severity
Catalyst efficiency degrades naturally with mileage and heat cycling until switching can no longer meet the threshold.
Common cause
Parts:catalytic converter
4
Failing downstream (post-catalyst) oxygen sensor
Medium severity
A lazy or biased downstream sensor can mimic a degraded catalyst; compare upstream/downstream switching patterns.
Common cause
Parts:oxygen sensor
5
Exhaust leak between the engine and downstream O2 sensor
Low severity
A leak lets outside air reach the sensor, flattening the switching pattern the PCM uses to judge efficiency.
Common cause
6
Exhaust manifold or downpipe gasket leak
Low severity
A leaking gasket ahead of the converter reduces exhaust pressure/flow through the catalyst and can introduce false air at the sensor.
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