Did it Saturday, and it was not as big as I feared. I just get really nervous messing with wiring because of the whole "point of no return" thing. The knock sensor on my truck has been bad since I last owned it in 2008. There was no MIL on the dash or anything, but I scanned it when I first got my scanner just for fun and found the code. Even back then, the relocation was pretty well established as a cheap fix for the problem.

For those not familiar with this, the knock sensor is located under the intake plenums on the back side of the engine. It's about a $25 part, but $800 of labor at a shop because of having to remove the upper and lower plenums. It detects cylinder knock (incorrect detonation of the air-fuel mix) and the engine computer adjusts timing and air-fuel ratio to compensate. The sensor in a Nissan plays a passive role, so the engine may run fine without it functioning, but it will throw a code. Some years ago, someone discovered that you could mount a new sensor and splice into the existing harness to avoid the headache of removing the plenums, so I followed their lead and did it.

This guy made a great how-to video on YouTube that I used to know what to do.
http://youtu.be/2t1l68s8MmM The only thing about his video that is not 100% clear is the location of the second wire. When you cut into the cover and find the black-covered wire, the second wire is wrapped around the white wire inside the black cover and not separately insulated. It took a few minutes for me to figure it out, but if you notice in the video when he starts the splicing, that splice looks like it's sticking out of the insulation - that's because he put the splice on exactly where it exits the cut he made. Also, the part number he lists is for the wiring harness, not the knock sensor. The sensor itself has a separate part number that I don't remember, but can supply if someone is looking to do this mod and needs the part number. (I bought a package deal off eBay for the harness and the sensor)

Overall, it's a relatively easy fix and should help my fuel mileage, since now the engine won't run rich to compensate for the bad sensor. Here are some pics of the finished product:

Knock sensor bolted onto intake with harness looped to left:


Prettied up where I did my splicing: (you can tell I recently replaced the valve cover gasket)

A bad knock sensor will not cause your truck to run "rich." It's job is to transmit a small voltage signal to the ECM when engine "knock" occurs; the ECM, in turn, retards the ignition timing slightly to help prevent engine damage. Knock sensors will typically not cause the MIL to illuminate unless the harness to it is shorted or open. A genuine Nissan knock sensor runs about $162; the high cost is due to "precious metals" that are used in the sensor. Pricing knock sensors, you will find them all over the map...from $25 all they way up to and beyond the cost of the genuine Nissan part. It would be interesting to know if there is a difference in the metals used in the genuine Nissan part versus the much less costly aftermarket, as well if there is any difference in the sensitivity of the sensor. It would also be interesting to know how much sensitivity is lost by the relocation of the sensor to the intake as opposed to be directly mounted to the top of the block. I'm not against the relocation procedure; I wouldn't want to pull up the intake manifold to get to the knock sensor, either! I would be interested in that information if it could be attained or determined.

I did some research into the potential downfalls of the relocation, and overwhelmingly what I came up with is that, if you live in populated areas in the US, Canada, Western Europe, or Australia, there should be no issue with knock due to the quality of fuel available. As I understand it knock will mainly occur when low-quality fuel is used, which is not the correct octane rating. As far as location, unless the knock is very very slight, it would register at that location just as well as the block. I'm measuring the mpg to see if there is a difference, as owners reported better mpg after doing the fix. I filled up yesterday at 14.6 mpg, so we'll see what happens with the next tank.

It would be nice if it did help the MPG...Pathfinders need all the help they can get!

It would be nice if it did help the MPG...Pathfinders need all the help they can get!

Amen to that!!

Update on mileage: I got 15.3 on my last tank, up from 14.6. I did a little more highway driving than usual on that tank, so I'll chalk up .3 mpg to that. Looks like the relocation got me close to a half a mile per gallon. Not great, (as if the mpg on these things was great to begin with, lol) but better than a kick in the butt with an iron boot. I'll take it.

I just did the same thing, but i didn't relocate it, i ripped both upper and lower manifolds off and put it in its factory location, using the factory harness.

Wasn't that hard, just time consuming.

I was going from a starting of 10.86 MPG, after two fill ups im closer to 12.6, while that sounds like an excellent improvement, my ultimate goal is to get her back up to the 16 mpg i was getting in the early summer.

So shes on her way to the shop, see if they can undo some of the finer adjustments i had them do, to fix the weird idle, and if that doesn't get me my MPG back, its new O2 senors.

-Kyle