P0420 code on 01 Maxima, 70K

I took my car into dealership to check it out, ... With that price its wise to get a second opinion.

What Nissan FSM says about the code, Possible Cause; see page EC-427 and read forward...

- Warm-up three way catalyst

- Exhaust tube

- Intake air leaks

- Injectors

- Injector leaks

- Spark plug

- Improper ignition timing

• Plug swap tst is easy DIY, swap three front plugs for test, total 6$

• if the FSM says plugs, also coils may cause bad spark; get one to test (50$?)

• ign timing check at a shop; 5$

• intake air leaks; various methods DIY tst; check all hoses

• If its possible to swap (dunno) the sensors from rear to front to tst, I'd try it first. If not, it is still possible to tst each sensor first, and compare them to rear sensors. If one seems to be problematic, replace only that one; not everything like stealer$hips likes (?) to do...

These mentioned other possibilities; did they read the manual? Its so much easier just to swap ALL and charge. (note! ...FSM does not even mention that O2 -sensor) Btw, click 'Favorite Links' at

In worst case they swap what they now say, and the problem sits in leaking injectors. You end up paying 2000$... Take care. Whatever parts is needed, they will be found lots cheaper in the net, 'any' car shop can do installation. Also O2 sensor change is very easy DIY.

The catalytic converter is covered warranty, 8 years or 80k miles.

You may need to pay for the O2 sensor.