Okay about a month ago i posted about having the codes 07 07 and 03 04.
i went to the mechanic for the knock sensor and he "cleaned" the knock sensor. He told me that knock sensors usually dont go bad, but they get dirty. Obviously i dont know anything because i bought it, and he only charged me 30 bucks.
so yesterday i was driving and i pressed the petal to the floor when getting on the freeway, my engine made a strange noise. I cant really describe it, just a really quick sharp growl kinda like i was over-working it towards the upper rpms. Ive heard it make this noise before (before i got my ks "cleaned"). It seems that the Check engine light came on right after this happened.
So the thing is, since the 02 sensor code (07 07) wont set off the CE light (or so ive been told). Something must be wrong with my knock sensor AGAIN.
can anyone tell me anything about this? can a knock sensor be cleaned? or is it expected that they go bad.
and any other advice?

also, when checking the codes i turned the ecu screw all the way to the right when the car was off, then i turned the car on. will this do any damage? The light was blinking but stopped, so i turned it to the left all the way and it did the code giving routine. Also, the engine seemed to rev after i turned the screw, like back to normal. It may have just been coincidence with the engine warming up and doing what it does, but im just curious if i did anything.
anyway, thanks. this is frusterating.

0. for starters, if the CEL is lit again, pull the codes and see what the ECU is complaining about.
1. the O2 sensor will set the CEL, it is the knock sensor that posts a silent failure
2. you can't clean a KS - you can clean the harness connectors and the grounds. I would recommend this anytime you have a KS code - just to make sure that those aren't the problems.
3. you can check the KS (550kohms) using the subharness
4. if you don't have a Haynes manual get one.
5. read the ECU code diagnosis instructions and follow them. It is not hard.
6. don't rush through the diagnosis - you are running around in circles. Slow down and take the time to figure out whats wrong.

Cheers.

okay the 02 sensor sets it off but not the KS? he didnt even touch the 02 sensor. the mechanic reset the ecu and the code didnt come on ,since he cleaned it, until just yesterday.
I have a haynes manual.
i already checked the codes i got 0707 and 0304.

That means your O2 sensor is bad. The KS is probably also bad too. You can check the KS using the method outlined in the Haynes. If you have never replaced the KS, its probably not a bad idea. You can pick up a KS for < 100 bucks from either Pinncle Nissan or JR Nissan right now - they have some special deals going. So to summarize:

1. Replace the O2 sensor (www.oxygensensors.com - get a Bosch OEM equivalent)
2. Check the KS - and probably replace. Be sure to check the subharness for continuity and clean the KS grounds (behind the fuel rail near the upper intake manifold).

Cheers.

thanks man.

if i were to replace my y pipe, would all these sensors still be used?

and do i need to buy certain tools to replace the 02 sensor?

You can use the same O2 sensors when you replace the y-pipe. Better yet, just wait until you replace the y-pipe (if you are doing it soon) to put in the new o2 sensor - that way you don't do the same thing twice.

You can use a open ended wrench or rent an O2 sensor socket set from autozone.

I would recommend posting in the regional forums and finding an org'er to help you out - for a price lower than a mechanic - since it seems as though you aren't a DIY'er just yet...

okay, thank you again.
I am capable of doing stuff myself. I mean, if adverage drivers can do it, i can do it. I just can't do it immediately since ive got a lot of other things going on. With the car and otherwise.

Good deal. Work slowly and carefully and it will go smoothlyl

oh yeah, this helps gas mileage, right?

The KS code almost always comes as a ghost code when an O2 goes bad.

Replace the O2 and clear the error codes, 90% of the time the KS code will not come back.

Find another mechanic, he took you for a ride when he "cleaned" your knock sensor.

i trust my mechanic, and i dont believe he took me for a ride considering i only payed him 30 bucks. He DID clean the harness or connectors or wahtever, my dad just told me. But i will get a new o2 sensor and check it all out. I still wonder why the o2 sensor wouldnt alarm the LIGHT for so long though when it did before.
and why is the knock sensor a ghost code? i thought i twas important.

Who told you the O2 was bad even though the light wasn't on... Your mechanic?
If so, please refer to my last post once again.

O2's are a very important part of the emissions system and will always set off the check engine light when they are not performing correctly.

The KS code almost always comes with an O2 code on our cars, thats just the way it happens. The KS by itself, if it's gone bad, will not set off the check engine light. Ask the engineers at Nissan why thats programmed like that.

The light was on, then I did the ecu code check and it pulled up 0707 and 0304. Which is an o2 sensor. Nobody told me that it was bad, it just gave me that code.
Is this sensor before or after the cat?