Igormac Car Service
CallWhatsApp
DTC DATABASE • OBD-II
P0420

Catalyst System Efficiency Below Threshold Bank 1

This page explains common reasons this code appears and what should be checked before parts are replaced.

Send This Fault CodeSearch another code
Common causes

What can trigger P0420?

  • Aged or damaged catalytic converter
  • Exhaust leak
  • Oxygen sensor issue
  • Persistent misfire or fuelling problem
Typical symptoms

What you may notice

  • Engine warning light
  • Often few drivability symptoms
  • Abnormal upstream/downstream O2 behaviour

Do not diagnose from the code alone

The code alone does not identify the failed part. Live data, wiring checks and manufacturer-specific subcodes may be required before replacing components.

Full scanLive dataWiring checksSensor plausibilityECU / module communication
Fast vehicle assessment

Need us to check your vehicle?

Send the registration or VIN, fault codes and a clear photo of the ECU label or warning message.

What do you need? Select all that apply

Emissions and motorsport-related software options are supplied only where lawful and appropriate for the vehicle's intended use. Road-legal requirements remain the owner's responsibility.

Your enquiry is saved securely in Netlify Forms and your configured email notification will alert IGORMACCAR SERVICE. For the fastest response, include registration, fault codes and clear photos.

WhatsApp