P0420 – Catalytic converter efficiency below threshold

System: Emissions - catalyst
Dashboard light: Check engine light (MIL)
Check-engine blink code: —
Applies to: 1SZ-FE (by platform)
Description: Catalytic converter efficiency below threshold
Possible causes: Trouble area: 1.Catalytic converter 2.Rear oxygen sensor 3.Exhaust leak
What to check: Checking points: 1.Check for exhaust leaks 2.Check rear oxygen sensor 3.Replace catalytic converter if worn
Confidence: medium (Toyota Echo 1999–2002 factory diagnostics, same XP10 platform; not confirmed on JDM 1SZ-FE)

From the factory service material. Clear the code and test-drive to confirm it returns. Search all fault codes · Common problems · Warning lights