← Back to OBD Codes

P0420 — Catalyst System Efficiency Below Threshold

Severity: Medium

Drive Advice:
Usually drivable for short distance unless flashing check engine light, overheating, severe misfire, or power loss.

Repair Cost: $20.00 — $2500.00
Repair Time: 20 — 360 minutes
Emissions / Smog: Likely Fail

Common Symptoms

  • Check engine light
  • Poor fuel economy
  • Sulfur smell
  • Low power

    • Common Causes

  • Exhaust leak
  • Bad O2 sensor
  • Misfire
  • Catalytic converter failure

    • Diagnostic Order

  • Check exhaust leaks first
  • Test O2 sensors
  • Check for misfires
  • Inspect catalytic converter last

    • Tools Required

  • OBD2 scanner
  • Multimeter
  • Smoke tester
  • Socket set

    • Brand Specific Notes

  • Toyota Camry: O2 sensor failure is common before catalytic converter failure
  • Ford F-150: Exhaust manifold leaks commonly trigger this code

    • Important Disclaimer

    Diagnostic results are informational only. Severity depends on vehicle condition and other fault codes.