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I know this trend has a lot of about it already I have read most all of the ones I can find. I bought a lexus RX300 from someone that told me it had 55k on a brand new motor and everything was good but knock sensor came up with in a day code 300. Fist attempt cheap ones on ebay worked for a day. Second attempt ones purchased on ebay from a place in CO that came out of a RX 300 1999 these worked great for about 120 miles then it would fault for both banks 325 and 330. It would reset and I could get about 60 to 80 miles then come back up with both then it would come up with only 325. While waiting for a new harness I installed a bypass to ride off both signals into one it worked for 30 miles. 

Through out all this I talked to the guy I got it from he said the car had sat for a couple year in a field what makes sense of the rats nest I found on top of the sensors The first time. So this I just spent the last two days redoing it again using the same sensors and a new harness. Using multimeter I have checked all the wirring to the sensors and the black and white wires to the computer. I set the meter to dc millivolts and beat on the block both banks would show voltage changing. But when I plug the connector into the one that feeds into main wiring harness and do the same test I get nothing on the pins that feed the computer the white wires in pins 3 and 4 show the voltage changing but those ground out to the connector on the back of the intake manifold. I get nothing on pins one and three. Do not have an ossiliscope to properly test. Thought with Both sensors failing then moving tto one it was probably the other after market wiring harness. 

Note the sensors I am using now have 71 on them the ones I pulled out orginally had 71N on them 

Other issues is that I am not even sure what year the motor is I was only told it was brand new timing belt done 45K ago.

After researching the pvc valve it had the new style metal one in it and they came out after 01 I believe. 

The valves had a lot of carbon build up on them cleaned all off at one point with bypass I was hitting 28mpg now I am hitting 12 to 14. 

Things I noticed during my testing through out looking at forums and other sites its says the shielding wires for to J10 I have no idea where that is but they ohm out to back of manifold. Not sure why I get nothing once the conecctor is connector to wiring harness unless the ecu is grounding them inside of it but the voltage will change when I move to white wires. 

One site I found says white wires connect to the computer not the back of manifold so maybe the 3.0 in this had a different set up then 1999 body. 

Since the car had sat for so long I have been running about four takes of premium first two with lucas gas treatment then one can bg44 last two with a little sea foam. 

I cant afford the oem sensors lost job due to no car thrn I got this and been beating my headd trying to figure out whats wrong the first time it was 330 after a while it was only 325 after the last new wringing harness install its back to both and only after two miles with the same sensors that were getting me 120 miles without code. 

If anyone has any input of other possible causes or where this J10 connector is to check out. I have also changed all the plugs and last time uses all new gaskets preformed a mfs cleaning and just got done doing the IAC cleaning lot of black stuff came out. Throttle body valves and intakes were all cleaned out first time around. 


Besides the rear brakes and doing thiese knock sensors three times there is a slight flicker in the gauges when I turn on the lights and not sure if its suppose to show a light on the dash but when I hit the power mode on gearshifter switch no light on das the snow one does work 


Please help I need top get this running right so I can get to work. and its getting cold I really don't want to do this again when its below zero with no garage. 

When the thing was running good with no codes it was great getting around through the woods and it got up and moved 

Also I did try swaping around some of the coil packs to see if it made any difference nothing 

When I finish getting it back together I was going to run some marvel mystery oil and sea form oin the oil for a day or so to see if maybe build up in the crank case is cccaudign them to go on and off

Right now I am so fed up with the car had it for 6 weeks and haven't been able to drive it much at all. Im at the pointI would just like to get the knock sensors to go away for so can sell it if need be but I don't have another car. 


I know this is long but I have been at this for weeks now cant find the difference between 71 and 71N same manufacturer to paroind to buy anything else off line due to all the fake stuff. And with all money out on other things can't swing the 298 x2 for new sensors from dealer along with gaskets and another two days of labor. 


why did the sensors work for awhile then not after new harness wand why when using multimeter does it stop at connector but work on other two pins and if the motor did only have 55k why knocks out already and not clearing up after all the fuel treamtment. 


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Hey! I don't know about the knock sensors yet, hopefully won't for a long time but, have you tried looking at the Club Lexus site for a solution?

Here is a link which may be helpful:


I have always found lots of useful information there, as well as this site.

Regarding your mileage of 12 to 14mpg after it being 28mpg: whenever you reset the computer the mileage will go higher then come down to match your driving habits, i.e., if you do mostly highway driving then you'll probably get higher mileage than if you drive in the city. After a computer reset I once showed about 48mpg, while I was on the highway and now it back down to 22mpg.

You may also want to perform a complete computer reset as I once did.

In the link below scroll down and you'll see what I did for a complete computer reset.


I hope some of this may help. Don't give up on your RX300. Also, although I haven't tried this yet, you may want to check out your Toyota Dealer and see what the costs are for some of your parts. If I had the money I'd go to Lexus and if I didn't have alot of money I'd go to Toyota.

Good Luck!  I wish for you the best. I know you'll get it done with the advice from both of these sites. Don't give up! Once you get it running properly you'll love it.

Take Care.



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