P0420 on a 2010 Chevrolet Equinox
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 2010 Chevrolet Equinox
Ranked from 784 NHTSA owner complaints filed for this vehicle.
- 1
Catalytic converter clogging/damage from chronic oil consumption
High severityOwners directly link this engine's factory oil-consumption defect to a clogged catalytic converter, and separately report converter failure codes and replacement needs alongside the same oil-burning problem.
Reported in 4 NHTSA complaintsParts:catalytic converter - 2
Catalyst overheating/damage from chronic misfire tied to timing chain/VVT wear
High severityOne vehicle was diagnosed with both a stretched/replaced timing chain and cylinder misfire at the same visit the catalytic converter was found to have failed; another owner's mechanic found over-advanced cam timing together with low catalyst efficiency.
Reported in 2 NHTSA complaintsParts:catalytic converter - 3
Failing downstream (post-cat) oxygen sensor
Medium severityOne owner reports replacing O2 sensors alongside catalytic converter issues, indicating the rear sensor itself may be degraded and tripping a false efficiency reading.
Reported in 1 NHTSA complaintParts:oxygen sensor - 4
Raw fuel contamination of engine oil from a leaking high-pressure fuel pump
Medium severityOne owner found a gasoline odor in the oil tied to a high-pressure fuel pump recall; fuel washing into the crankcase and unburned fuel reaching the exhaust can foul a marginal catalyst.
Reported in 1 NHTSA complaint - 5
Worn or aged catalytic converter
Medium severityNormal thermal aging reduces oxygen storage capacity over time until the converter can no longer meet the efficiency threshold monitored by the rear O2 sensor.
Common causeParts:catalytic converter - 6
Exhaust leak upstream of the rear O2 sensor
Low severityA leaking manifold, gasket, or flex-pipe ahead of the converter draws in outside air, skewing the rear sensor's efficiency reading.
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.