How to test a knock sensor?

Post by **JPG0511** » Wed Jun 15, 2005 3:38 pm

I have a code for the knock sensor on my 93 hb 240. And the only thing I can find on testing the sensor is to check the conection for the wiring harness and check that it is grounded to the engine block. And both are ok. Is there any other check I can do before I buy a $100 sensor? Thanks for any help you can give.

Post by **navysnail** » Wed Jun 15, 2005 5:31 pm

i dont think there is any way to check it, but i will look in the fsm to see if there is any way to.

Post by **slipnfall** » Fri Jun 17, 2005 9:08 am

No there is no easy way to test a knock sensor. They are a piezo-electric sensor, which can only be tested by exciting them with a frequency sweep(and typically high voltage). Each differenty type of sensor has different frequency 'modes', which is steps of frequency at which they will resonate. Even knowing the exact modal frequencies of a piezo electric actuator/sensor, it is still very hard to distinguish mechanical stresses and fractures in the material.

Easy answer is, 'no', sorry. If it's bad enough that the ECU is telling you it's bad, then there's no point in diagnosing further. Definately check continuity on all wires from ECU to the engine room harness(for the sensor), before buying a new one.

Post by **JPG0511** » Fri Jun 17, 2005 11:58 am

Also my check engine light works but does not come on with the sensor unplugged. I drove it some with it and the TBS unplugged just to se if it would come on. It had the codes stored in the computer but the light never come on.

Post by **Q45tech** » Sun Jun 19, 2005 3:49 am

Knock sensors on pre OBD2 engines don't illuminate check engine lights just set codes........Consult scan tool required.

Examine Knock sensot for tiny hairline cracks in black plastic covering......fails from overheats to plastic! Changes frequency response /sensitivity when cracked.550,000 ohms [+-] 5%/

Just a normal maintenance replacement item every 6-10 years.

Post by **kool-aid54** » Mon Jun 20, 2005 4:02 pm

a friend who is a mechanic said that if you shake a knock sensor it will rattle a little. The bad one he had wouldn't rattle. Does this work on all cars or is it car specific?

Post by **w1ngzer0** » Wed Aug 10, 2005 4:11 pm

Where is the knock sensor? is it just the o2? or are they 2 different things. I gotta learn somehow

My friends 240sx is throwing a 34 and i don't know the location of the knock sensor. Then later we ran it @ 2k rpm and turn it off then the ECU threw a 55....

Also when you rev it then let it drop in revs it dies.

Post by **BadMojo** » Wed Aug 10, 2005 4:33 pm

w1ngzer0 wrote:Where is the knock sensor? is it just the o2? or are they 2 different things. I gotta learn somehow

My friends 240sx is throwing a 34 and i don't know the location of the knock sensor. Then later we ran it @ 2k rpm and turn it off then the ECU threw a 55....

Also when you rev it then let it drop in revs it dies.

On the KA24DE the knock sensor is inconveniently tucked away under the exhaust manifold. Nistech tells me it can be reached from below the engine by removing the oil filter.

The O2 sensor is in the exhaust manifold.

Code 55 is ECU-talk for "everything's A-OK", FYI.

Post by **w1ngzer0** » Wed Aug 10, 2005 9:33 pm

After we ran for a minute or 2 @ 2k rpm running hella thick. Turned it off, Ran a 55.

We went back out there with the ignition in the on position without turning on the motor and still threw a 34.

So, with what im discribing does it sound like the knock sensor? its throwing a 34 with the ignition in the on position. Runs hella thick and stalls.

Post by **w1ngzer0** » Wed Aug 17, 2005 11:41 am

does anyone have a picture of where its at?

Post by **BarnDog296** » Fri Feb 16, 2007 5:00 am

I am having the same problem myself, where it is reading as a 34 code, then a 55. I think the knock sensor is messed up but maybe not all the time, like sometimes its right? but I honestly have no clue. I am about to replace mine also, so i feel your pain. The cheapest I have found them is about $150 but general places sell them for like $230, thats too much for a sensor... Its practically rape.It is also in the WORST place ever In the center of the engine under the intake manifold. now the intake manifold wraps under too, so its a ***** to get at it from underneath also. Anyway, here is a pic of where it is for anyone who needs it.

Also, a pretty good write up on how to replace it: http://www.socal240sx.org/articles.html

Biggest PITA ive ever seen..... specially for a sensor...

I thought I read that Jim Wolf Technologies had better results in their tuning by relocating it somewhere else, but some ppl say they did that for ease of replacement, and it actually hurts the performance of the sensor.

Does anyone know anything about this at all? Or where they moved it to?

Post by **Defiant** » Fri Feb 16, 2007 3:04 pm

The middle of everything like that is the best location, but anywhere that's tight against the block, or under a bolt that threads into the block will suffice. The block is much like a bell, and the sound the sensor is listening to will conduct through it.Somewhere, hiding from the search engine, on a Z site someplace there's a good description of moving it out from the factory's diabolical under-the-plenum location to a place actually accessibly by humans weilding wrenches. Good luck trying to find the article again.

Post by **OM3GA** » Sun Feb 18, 2007 5:46 pm

They might have put it under there so nobody would hit it with anything since its such an expensive sensor,That would be my guess is that its under there so it can be protected,Just like the solenoids for the egr and stuff are on the back of the head pita to get to but those are $130 a piece.

Post by **mrbizness1** » Sun Feb 18, 2007 6:05 pm

before you change the knock sensor there is one other thing to look at. I have a 98 alty, behind the l/r wheel there is a canister that recycles emissions fumes. Attached to it is a pump, remove it and look into the end you will see a small plunger, you should be able to move the plunger with a small screw driver. If its frozen then it can give off a code and also make a knock sensor code come on. After I changed this both codes went away.Ebay has knock sensors for under $100.00

Post by **Q45tech** » Mon Feb 19, 2007 4:53 am

Knock sensors fail from being over heated! They are rated for a maximum of 150C [275F].......................a single overheat can begin the housing cracking process.

Careful about buying junkyard or used units without a magnified examination for tiny hairline cracks and resistance check..................used is used and they have a limited operational life.

Post by **mrbizness1** » Mon Feb 19, 2007 12:42 pm

plenty of OEM knock sensors here, even cheaper than when I bought mine 9 months ago.

http://search.ebay.com/search/...ensor

Post by **maj Andres** » Sat Jan 19, 2008 6:35 pm

JPG0511 wrote:Also my check engine light works but does not come on with the sensor unplugged. I drove it some with it and the TBS unplugged just to se if it would come on. It had the codes stored in the computer but the light never come on.

does your check engine light have a lightbulb? mine didn't

Post by **lucasjsr** » Fri Jan 25, 2008 6:22 pm

I bought a 95 Maxima w/155K miles that had been sitting for a while. I have been getting it shape (1/2 shafts, spark plugs, oil change, brakes and rotors, new #4 injector and temp sensor and bank 2 #1 O2 sensor). I have a problem with the check eng light flashing then setting a #3 cylinder misfire but I think that has cleared up after a tank of gas with BG44K cleaner. I still have a slightly rough idle and minor missing but no chk eng light. Could this canister you described cause any of my current problems? Do you have any idea where the canister may be found on a 95 Maxima? DO you know if an ODB2 will set a KS code without setting the Ck Eng light? Can a KS cause a rough idle? Also I noticed when standing on the driver’s side of the car to the left of the air filter there is a larger hose (aprox 1") and a smaller hose (aprox 1/4"). They are harnessed/clipped together. The smaller hose is not connected to anything and I have not idea if it is supposed to be that way or not. I have discovered the smaller hose has what I believe is a check valve of some sort in it. I am also getting pretty poor gas mileage. At full throttle it runs out fine. Any and all help is appreciated

Post by **cretney** » Sun Aug 09, 2009 9:36 am

I have a 1996 Nissan Altima, and about 2 years ago, it started to rough idle. After some internet searching I stumbled on an issue that seems to plague the Altima. The intake manifold gasket apparently fails, and now your air/gas mixture is thrown off, causing the car to idle poorly.

To diagnose the problem, it is fairly simple. Using a propane torch (do not light your torch, just gas...in case you were wondering), you can search around the intake manifold. So, with the car idling, just shoot the propane gas around the intake manifold gasket area, until you notice that the rough idle begins to go away. As you remove the propane from a specific area, the rough idle returns.

Unfortunately, the replacement of the intake manifold gasket is not a simple task, and requires removing a ton of components. I usually would take on most repairs, but this just appeared to be a real headache and decided to pay a pro.

It cost me $550 to get the repair done. It seems to have done the job, and my car is now running fine at 207,000 miles. Except now, my O2 sensor rusted out of my catalytic converter, and I am attempting to repair using a high temp adhesive. I also got the knock sensor code, but I am hoping this may just be a stored code, that will go away after I fix the O2 and get the codes reset.

Post by **saipan240** » Sat Jan 16, 2010 12:05 am

Hi, I have the same problem. I diagnosed my car and the code it gave me was number 34 which was the knock sensor. We also opened the ecu box and we found out there was a fried/burned part in the ecu. do you think I would have to change the whole entire ecu or is it repairable? Thanks

How to test a knock sensor?

How to test a knock sensor?

Re: (240kid)

Re: (slipnfall)

Re: (JPG0511)

Re: (w1ngzer0)

Re: (w1ngzer0)

Re: (Defiant)

Re: (BarnDog296)

Re: (mrbizness1)

Re: (Q45tech)

Re: (JPG0511)

Re: (mrbizness1) EMmission Canister Question

Re: (mrbizness1) EMmission Canister Question (lucasjsr)

Re: How to test a knock sensor? (JPG0511)

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