P0420 on a 2016 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 2016 Chevrolet Equinox
Ranked from 392 NHTSA owner complaints filed for this vehicle.
- 1
Catalytic converter fouled by chronic oil consumption (2.4L Ecotec design defect)
High severityThis engine's well-documented oil-burning problem (many owners report quarts consumed with no external leak) lets oil ash coat and poison the catalyst, dropping its efficiency below threshold.
Reported in 11 NHTSA complaints - 2
Timing-chain-jump misfire damaging the catalyst substrate
High severityComplaints describe the timing chain jumping/snapping and causing cylinder misfire and warped pistons; sustained raw-fuel misfire overheats and melts the catalyst substrate.
Reported in 3 NHTSA complaints - 3
Exhaust manifold leak ahead of the sensor
Medium severityA cracked/failed exhaust manifold introduces false air into the exhaust stream, skewing the catalyst monitor's readings.
Reported in 1 NHTSA complaint - 4
Natural aging/wear of the catalytic converter
Medium severityPrecious-metal washcoat efficiency degrades with mileage and heat cycling until it can no longer meet the OBD threshold.
Common causeParts:catalytic converter - 5
Failing downstream (rear) O2 sensor
Medium severityA lazy or biased downstream sensor can make a healthy catalyst look inefficient to the PCM.
Common cause - 6
Coolant intrusion into the catalyst from a head gasket failure
Medium severityCoolant burned through a leaking head gasket deposits silicates on the catalyst, poisoning it.
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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