P0420 on a 2016 Jeep Patriot

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 2016 Jeep Patriot

Ranked from 455 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Repeated misfires from camshaft/crankshaft sensor faults overheating the converter
High severity
This fleet has well-documented camshaft/crankshaft position sensor failures (recall S89) causing misfires; sustained misfires dump raw fuel into the exhaust and can overheat/damage the converter.
Reported in 4 NHTSA complaints
Parts:camshaft position sensor crankshaft position sensor
2
Worn/failing catalytic converter (repeat failure)
High severity
One owner had the catalytic converter fail again only a few years after it was replaced under an earlier recall, and another had a converter failure independently diagnosed.
Reported in 2 NHTSA complaints
Parts:catalytic converter
3
Failing downstream (post-cat) oxygen sensor
Medium severity
A biased downstream O2 sensor can mimic a failing converter's signal even when the cat itself is still within spec.
Common cause
Parts:oxygen sensor
4
Exhaust leak upstream of the downstream O2 sensor
Medium severity
A leak before the sensor lets in outside air that skews the efficiency comparison the PCM relies on.
Common cause
5
Oil or coolant contamination of the catalyst
Medium severity
A leaking valve seal or gasket can coat the catalyst in combustion byproducts that poison its efficiency.
Common cause
Parts:catalytic converter
6
Damaged or loose exhaust joint near the sensor
Low severity
A leaking clamp or damaged exhaust section can admit outside air that fools the efficiency monitor.
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