P0420 on a 2015 Chrysler 200
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 2015 Chrysler 200
Ranked from 1,983 NHTSA owner complaints filed for this vehicle.
- 1
Recurring catalytic converter failure
High severityThis vehicle had its catalytic converter replaced once already after the original failed and damaged the engine, and the replacement converter is now failing again — a documented recurring pattern on this specific car.
Reported in 2 NHTSA complaintsParts:catalytic converter - 2
Long-term unresolved misfire damaging the catalyst
High severityA manufacturer-acknowledged misfire (per TSB) and a separate unresolved cylinder-4 misfire both went unfixed long enough to be linked to major engine/exhaust damage on this platform.
Reported in 2 NHTSA complaints - 3
Failing downstream oxygen sensor
Medium severityOwner reports recurring shop visits for an O2 sensor tied to a persistent check-engine light.
Reported in 1 NHTSA complaintParts:oxygen sensor - 4
Oil contamination of the catalyst from an oil cooler/gasket leak
Medium severityDealer diagnosis on this vehicle found a failed oil cooler housing leaking a significant amount of oil directly onto the engine, a known way to contaminate/foul a downstream catalyst.
Reported in 1 NHTSA complaint - 5
Weak fuel pump contributing to rich/lean swings that stress the converter
Low severityFuel pump replacement was required on this vehicle after a misfire/check-engine event, and unstable fuel delivery accelerates catalyst wear.
Reported in 1 NHTSA complaintParts:fuel pump - 6
Worn/aged catalytic converter (mileage-related)
Medium severityCatalysts lose efficiency with age and mileage independent of any specific failure event.
Common causeParts:catalytic converter - 7
Exhaust leak upstream of the sensors
Low severityA leak in the manifold or front pipe dilutes the exhaust sample and can present as reduced catalyst efficiency.
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.
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