how do i run i self diagnostic test?
on my 1991 maxima

 

and wharts a knock sensor

 

and wharts a knock sensor

 

I could run thru ALL the steps with you, but I'm kinda rusty myself. Go out and buy either a Factory Service Manual (FSM) or get a Chilton's/Haynes manual. They have steps for getting into the correct CEL diagnostic mode.

Knock sensors, if I'm not wrong, exist onlly on the 3.5Gens (ie the VEs).

 

You're wrong.