mechanical help

[luis k]

2006 maxima code p0420

[Timothy S]

p0420 is a catalytic convertor efficiency below threshhold. Means your catalytic converter is going out. Whether you change it sooner or later depends on local emissions testing laws.

[NutriaforBreakfast]

My car's cat is 21 yr old
Do you have history with this car?
If the engine has been well maintained it doesn't seen like it would need it
Could this code have popped up if there has been an air leak in the exhaust?

[Timothy S]

The rear o2 sensor is switching when it should stay high, so there is probably too little oxygen content in the exhaust. A leak would probably make your cat look more efficient. It might be running too rich due to vacuum leaks, or have o2 sensor problems. A scanner with live data can show the oxygen sensor readings and fuel trim. That would give us clues for the next step in the diagnosis.