Reply To: can bad plugs cause faulty cat readings?

[Richard Kirshy]

If the plugs are correct and properly gaped.
Then your left with the following possible causes:\
Faulty oxygen sensor
Faulty air-fuel sensor
Worn or internally failing catalytic converter (Most Common)
A leak in the exhaust system
Misfire (the root cause of converter failure)
Rich or Lean air-fuel ratio (the root cause of converter failure)