P0420 on a 2017 Jeep Renegade

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 Jeep Renegade

Ranked from 560 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Worn or failed catalytic converter
High severity
Three separate owners of this exact vehicle had P0420 confirmed by scan tool or auto-parts diagnostic and were specifically told the catalytic converter had failed — one explicitly noting the same defect as a recall issued for earlier model years that excludes their 2017 VIN.
Reported in 3 NHTSA complaints
Parts:catalytic converter
2
Oil/coolant contamination of the catalyst from a head gasket or internal engine leak
High severity
One owner's engine failed to restart and was diagnosed with coolant intrusion into a cylinder; burnt coolant reaching the exhaust will contaminate and damage the downstream catalyst.
Reported in 1 NHTSA complaint
3
Excessive oil consumption fouling the catalyst
Medium severity
One owner's Renegade stalled while consuming excessive engine oil; oil that reaches the exhaust coats and poisons the catalyst over time.
Reported in 1 NHTSA complaint
4
Catalyst substrate damage from a chronic misfire
High severity
One owner reported severe multi-cylinder misfires under load; unburned fuel reaching the converter overheats and can melt the substrate.
Reported in 1 NHTSA complaint
5
Failing downstream oxygen sensor
Medium severity
A sluggish post-catalyst O2 sensor can read like a dead converter even when the catalyst itself is still functional.
Common cause
Parts:oxygen sensor
6
Exhaust leak ahead of the downstream sensor
Medium severity
A leaking gasket or joint before the sensor dilutes the exhaust sample with outside air, mimicking poor 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.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Check Engine Light