P0420 on a 2013 Chevrolet Cruze
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 2013 Chevrolet Cruze
Ranked from 585 NHTSA owner complaints filed for this vehicle.
- 1
Coolant/oil intrusion from chronic head-gasket and coolant-system failures
High severityThis generation Cruze (1.4L turbo) has widely documented head-gasket and water-pump failures that let coolant or oil into the combustion/exhaust path; several owners here describe head-gasket failure with oil and coolant mixing, which coats and kills the catalyst.
Reported in 4 NHTSA complaints - 2
Ignition misfire (worn spark plugs/coil pack) overloading the catalyst
Medium severityOne owner reports a rattle, tailpipe smoke, and a CEL for a misfire code with loss of power shortly after a plug/coil service; raw fuel from a misfire is a known catalyst killer.
Reported in 1 NHTSA complaint - 3
Worn or degraded catalytic converter
High severityHigh-mileage catalyst substrate loses oxygen-storage capacity over time; confirm with a rear O2/AFR sensor switching-rate test versus the upstream sensor.
Common causeParts:catalytic converter - 4
Exhaust leak ahead of the catalyst or sensors
Medium severityA leaking manifold gasket, cracked manifold, or loose flex-pipe joint upstream lets outside air skew the O2 readings and falsely trips a catalyst-efficiency code.
Common cause - 5
Failing downstream (post-catalyst) O2 sensor
Medium severityA lazy or biased rear O2 sensor can mimic reduced catalyst efficiency even when the converter itself is fine; compare live rear sensor activity to the front sensor.
Common causeParts:oxygen sensor - 6
Rich or lean fuel trim from a vacuum leak or dirty MAF sensor
Low severitySustained rich or lean operation prevents the catalyst from cycling in its efficient window; check long-term fuel trims.
Common causeParts:mass airflow sensor
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.