code po400 is it a serious problem?

 

Hi,first time here,I didnt want to make new post about check engine light.One question
Is there any way to diagnose check engine light manually for 1997 protege.I have 97 maxima and there is computer under the dash,and its very easy to check the problem when the light is on, not sure if thats possible for proteges.

 

I think 0400 is catalist efficiency or something,Clearit and see what happens. Should not be a problem