P0420 on a 2013 Toyota Camry

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 Toyota Camry

Ranked from 301 NHTSA owner complaints filed for this vehicle.

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1
Excessive Oil Consumption (2AR-FXE / 2AR-FE Engine)
High severity
Low-tension piston rings stick, causing oil to bypass into the combustion chamber. Burning oil coats and destroys the catalytic converter, triggering the P0420 code.
Reported in 2 NHTSA complaints
2
Damaged Wiring Harness (Rodent Damage)
Medium severity
Rodents chewing on engine wiring can damage O2 sensor circuits, causing communication failures and triggering engine codes. Confirmed by visual inspection of the wiring harness for chew marks or nesting materials.
Reported in 1 NHTSA complaint
3
Catalytic Converter Failure
Medium severity
The catalytic converter is no longer efficiently reducing emissions, often due to age, contamination, or internal degradation. Confirmed by checking upstream and downstream O2 sensor readings for mirroring.
Common cause
4
Faulty Downstream Oxygen (O2) Sensor
Low severity
The post-catalyst O2 sensor may be degraded, sluggish, or failing, falsely reporting that the catalytic converter is inefficient. Confirmed by testing sensor response time and voltage output.
Common cause
5
Faulty Upstream Air/Fuel Ratio Sensor
Medium severity
An inaccurate upstream sensor can cause improper fuel mixture, leading to poor combustion and false catalyst efficiency readings. Confirmed by checking fuel trims and sensor voltage.
Common cause
6
Exhaust Leak
Low severity
A leak in the exhaust system near the O2 sensors can introduce unmetered oxygen, skewing the sensor readings and triggering a false P0420. Confirmed by visual inspection and listening for exhaust ticking.
Common cause

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