Error code

OBD2 P0420

OBD2P0420
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Catalyst System Efficiency Below Threshold.

Severity

severeDo not drive the car as it could be immobilized or catch fire.

Summary

P0420 indicates that the catalytic converter on Bank 1 (the bank containing cylinder #1) is operating below an acceptable efficiency threshold. This code affects emissions and can lead to serious issues if not addressed.

Symptoms

  • Illuminated warning light
  • Potential failure during emissions testing
  • Increased fuel consumption
  • Engine may idle roughly or lose power upon acceleration

Common Causes

  • Catalytic converter failure due to long use
  • Use of poor quality fuel
  • Exhaust leaks in components like exhaust manifolds and down pipes
  • Mechanical issues causing excessive oil consumption
  • Unauthorized PCM programming or illegal exhaust modifications

Diagnosis

  1. Check for other related codes and address them first.
  2. Verify PCM programming is in stock condition.
  3. Inspect exhaust system for leaks or restrictions.
  4. Measure catalytic converter temperature with an infrared thermometer.

Fixes

  • Replace the faulty catalytic converter.— $2000

FAQ

Will catalytic converter cleaner fix P0420?

No, a cleaner will not resolve this issue as it indicates a failed or failing catalytic converter.

Does P0420 affect performance?

Yes, it can cause rough idling and power loss upon acceleration.

Could P0420 be an O2 sensor issue?

While oxygen sensors are involved in monitoring the converter's efficiency, this code specifically indicates a problem with the catalytic converter itself.

Will P0420 cause limp mode?

It is unlikely to trigger limp mode directly but can affect driveability and emissions compliance.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

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