For Shop Owners
AutoCodes
OBDII Code List
P0420 1997 HONDA CIVIC

P0420 1997 HONDA CIVIC - Catalyst System Efficiency Below Threshold Bank 1

Repair Importance Level: 2/3
Repair Difficulty Level: 2/3 What does this mean?

Possible causes

  • Three way catalyst converter Bank 1
  • Bank 1 sensor 2 oxygen sensor (Secondary HO2S)
  • Exhaust tube
  • Intake air leaks
  • Fuel injectors may be faulty
  • Fuel injector leaks
  • Spark plugs may be faulty
  • Improper ignition timing
  • Engine Control Module (ECM)
What does this mean?

Tech notes

As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.
What does this mean?