My SES (Service Engine Soon, my light says that and NOT Check Engine Soon, I guess some people call it CEL for Check Engine Light , oh well same thing :> ) came on recently, again.
3 codes.
Knock sensor
420 cat code
Knock sensor

The dealer swears up and down they have almost never, ever replaced a knock sensor on anything. Like it is impossible for it to be the knock sensor. I am still under my extended warranty for a little while longer and want it replaced. My understanding is all my dealer does is check the KS with a voltimeter, period.
Should they be checking my degree timings for the ECU?
What else should a nissan dealer be doing verify the knock sensor is not my problem?
They insist that never, ever will a SES signal that a KS has gone bad, period.
I have to go to this dealer if I am within 50 miles of it.

All I know is that my car is SLOW now, 2 (older z24 styles) cavaliers beat me/stayed even since this light has been on.
My car has about 95k.

 

My buddy at the Nissan dealer used a handheld computer to diganose it. It's called a "Consult II". Besides we all know better when it comes to the KS going bad. . . just do a search . . . it happens quite often with our cars.

 

The KS can be tested without removing it in a few seconds by measuring the internal resistance at the sub harness connector (550 k-ohm). The dealreship should have no problem doing this for you.

The OBD-II scan tool mentioned above reads the codes from the ECU (you can also do it yourself with only a screwdriver). Sometimes the ECU will give a KS code caused by another failing part (even though the KS is not bad).

If you look back at the archives you will see that MANY members have had to replace a bad KS (including myself on both mine and my wifes Maximas).

A car that is sluggish below 3000 RPM is a pretty good indication of a bad KS. Incidentally, the intake manifold does not need to be removed to replace the KS (as the shop manual indicates). It can be done in 20 minutes by an experienced mechanic.

Here is my standard KS reply:

Once and for all: a bad knock sensor WILL NOT trip the check engine light, you must extract the codes from the ECU to determine if your sensor is (potentially) bad (code 0304). Some other hints as to a bad KS: poor acceleration below 3000 RPM (I was getting tired of being left behind at stoplights by Honda Civics).

If you don’t already own a Haynes or Chilton manual, get one. In addition to telling you how to extract the codes and locate the KS, there is a wealth of useful information for the do-it yourselfer. I am very cheap, but this an area well worth spending the $20 or so (I bought mine off of EBAY for $10 shipped).

The ECU is located behind the center console on the drivers side. It is accessible by removing the plastic cover panel right next to the gas pedal. The ECU is a metal box with a screw on the side covered by a piece of tape. Peal back the tape to get at the screw. With the ignition in the “On” position, turn the screw all the way clockwise, hold for at least 2 seconds, turn it all the way counterclockwise. Your CEL will now start flashing out any codes stored in the ECU. The codes are two digit numbers. The first number is signaled by long flashes, there will be a two second pause, and the second number will be indicated by a series of short flashes. Long-long-long-pause-short-short-short-short = 0304 (KS fault). There may be more than 1 code in the ECU, they will be flashed out sequentially and the whole sequence will repeat. To clear the codes from the ECU, follow this sequence: clockwise, hold, counterclockwise, hold, clockwise, hold, counterclockwise.

A good KS will measure ~550 k-Ohm resistance between the left pin of the KS and ground. You can check the resistance without removing the KS by following the harness to the connector. The connector has two pins, only one of them hooks up to the KS, so try them both. The act of whacking on the KS with your wrench can (temporarily) start it working again, so checking the KS once you removed it may not give you the bad reading you suspect. Hint: the connector is not the green one closest to the KS (1995-1996 models – most likely 1994-1999), it is a few inches closer to the front of the car. A heat shielded wire leads into the bottom of it and there are two wires coming out the top, one clear and one black.

Low cost knock sensor sources: The dealer will charge you $160 or so for the sensor. I purcahsed a Nissan OEM sensor off of EBAY for $90 shipped. I have seen them for as little as $80 and routinely for $100-$110. Search for both “Maxima knock” and “Nissan knock” to make sure you get all the possible matches. You can get a Bosch sensors for $115 shipped from http://www.nissanpartstore.com/nissan_knock_sensor.html I prefer OEM parts when possible and have no information on the Bosch.

Two good article on KS replacement:
http://www.skippynet.com/maxima/knocksensor.htm
http://www.motorvate.ca/mvp.php/507


Modifications to the Skippynet method

The article suggest using a 14” (or longer) ¼” socket extension to reach the KS retaining bolt. I found that using a 9” extension made it much easier to get the u-joint onto the KS bolt. To save money, I used two 3/8” drive extensions with a 3/8 to ¼ adapter, a ¼” drive u-joint and a ¼” 12mm socket (most of which I already had). Skippynet suggest using a 12mm flex socket, but being cheap I used a separate socket and u-joint so that I would have a more useful general purpose tool left over than the 12mm flex socket (better yet, I borrowed the u-joint and saved another $8). A 3/8” u-joint is a slightly bigger animal and in my opinion would make it hard to get the socket onto the bolt. It was not at all difficult to loosen the bolt using this setup. I had also borrowed a 16” extension and found it very difficult to get the socket onto the bolt head (I gave up after about 2 minutes, so it probably could have been done).

Once the bolt was out, I used a magnetic pickup to retrieve it (and eliminate the possibility of dropping it into the engine cavity where as you will find out soon, is not a very friendly place). With the bolt removed, you can pull the knock sensor out of the cavity by the harness and replace it. Next, I put the bolt into the new KS and used a small piece of tape to hold it in place while I stuffed it back into the engine cavity (again to eliminate the chance of dropping it in there).

Now the difficult part: I don’t see how you can locate the bolt into the hole and get it started without stuffing your hand under the manifold (others have done it using a claw type pickup to position the bolt). If you have very large hands, you might try enlisting a girlfriend or your mom as others have done. I was able to get my hand in there and get the bolt hand tight, then it was just a matter of using the 9” extension/u-joint setup again to do the final tightening. Your hands will get cut up a little doing this, but no worse than I am used to with other auto repairs.

I was able to replace the KS in both cars in less than 1 hour including test drives using this method. The real key is using the skippynet socket extension method to crack the bolt loose. Once you have jammed your hand into the engine cavity you will realize how difficult it would have been to get a wrench on the bolt and loosen it.

 

Thanks for the reply, I have searched and read a lot about the knock sensors and ECU code reseting etc. My dealer will not replace it under my exteneded warranty because they think nothing is wrong with it. That is my problem. I imagine all they do is measure the internal resistance and they are done and say "sorry it is due to your custom exhaust system throwing code 420 and thus the KS piggybacks on that code,etc."

So everyone that has replaced their KS means their KS would fail the internal resistance test? No other test that guarentees failure of the KS?

 

Nice post gansemer! lots of good info in there

 

You can disconnect the KS at the aforementioned sub-harness. If the KS is good, you should be able to feel the loss of power below 3000 RPM(although other problems may mask it). There are no other positive indicators of failure except the resistance test.

 

The KS may be checked with an ohmmeter.

1) Raise the hood. View the engine from the driver's fender. Look into
the deep valley between the cylinder banks and below the intake manifold.
Identify the KS as a black item fastened to the block by a single vertical
bolt. A wire harness wrapped in black leads toward you, out of the valley.
That is the KS sub-harness.

2) Follow the KS sub-harness to it's nearest connector. This is connector F121.
It is located near the upper right-hand corner of the valve cover of the forward cylinder bank, as viewed from the front of the car.

3) Disconnect F121. You have to do a "press the latch and wiggle and
pull" to disconnect it. F121 has only two pins; if you see more than two
pins, you have the wrong connector. Use a digital ohmmeter capable of
measuring more than 10 Megohms. You want to measure the pins of F121, not
the sockets of the matching connector. Measure the resistance between a
good ground (such as the battery negative terminal) and pin #2 of connector
F121. On my car this is the highest of the two pins, the one closest to
the front of the car. The factory spec is 500 - 620 Kohms.

The manual says you have to remove the intake manifold to replace the KS. However, I think that a person with good dexterity and a 10mm ratcheting box wrench could replace the KS without disturbing the manifold.

Important note: the dealer can do a more thorough test with his CONSULT electronic tester. The resistance test described here is a useful but limited test. A Knock Sensor which fails this test is definitely bad. However, a KS which passes this test is not guaranteed to be good.


0304 from my sig

 

Realize however that even a bad KS may have 550k going through it. It's been posted many times...

 

Many people have told me that you never need to change the knock sensor ever. Usually something is causing the knock sensor to go off. Might want to check ignition packs, spark plugs, or O2 sensors.

 

It is often the case that another failure will give a false KS code, so it is usually recommended to fix other ECU codes first. I can personally verify that I got increased power and fuel mileage after replacing my KS (that tested bad and set off only a KS code). Many others on this forum will back this up. You never need to replace the knock sensor ever if you don't mind a poor performing Maxima.

I am suspect of any information containing never...ever.

 

Hey All,

Something didn't seem quite right on the car. It just seemed very sluggish and didn't run as powerful as a "Maxima" should, so I did the self diag and got code 34. After many hours of research and ohm meter tests, etc, I orderd a new Knock Sensor from courtesyparts.com They seem to have some nice prices by the way.

The question is, do you guys know what causes a knock sensor to go bad. It seems like everyone know's how a working KS will help your car, but I haven't seen any posts on what may have failed to damage the KS.

95max