اردو
DTC Codes / Powertrain

P0420 — Catalyst System Efficiency Below Threshold (Bank 1)

Powertrainmedium

The oxygen sensor after the catalytic converter reads almost the same as the one before it, so the converter is not cleaning the smoke well.

Symptoms

  • Check engine light
  • Car usually drives normal
  • Fails emission test
  • Sometimes rotten-egg smell

Common causes

  • Worn catalytic converter
  • Exhaust leak near the rear O2 sensor
  • Faulty rear O2 sensor
  • Misfire or rich running damaged the converter

How to fix

  1. Fix misfire or fuel codes first
  2. Check for exhaust leaks
  3. Check rear O2 sensor data
  4. Replace the converter only after the above

Can I keep driving?

Yes for now; repair soon.

These are the general meanings. Some companies use a code a little differently — confirm with a scanner and your car's service manual.