pfd FSM available on this site
http://www.nicoclub.com/FSM/quest/2004_Quest/
then to find the specific part/ section:
idx. pdf
then it should direct you to section EC-187 and EC-200
but that whole section is a good read; page EC-27 sorta gives you where it is <shrugs>
ps, don't be throwing parts at your vehicle trying to fix something that may be good; whats the problem? so follow those tests on the pages to rule it out first