I have read several discussions as regards Knock Sensors (KS). If someone could help me, I would be most appreciative. I have a 99 RX300 with 157,000 miles. The check engine light recently came on and the scanner says it is a KS code (PO330). After reading the forum, I replaced the timing belt, belt tensioner, etc. I also changed the water pump and other belts. Having completed the work, I cleared the code, and all was fine for approximately 50 miles. The KS code returned. The engine runs smooth with no noticeable knocks, pings etc. Much like others on the forum, when the check engine is on, the transmission does not always shift into OD. Please hang in here with me for my question(s).

I have noticed something that I cannot understand. On three separate occasions, when the fuel level reaches approximately 1/8 of a tank, the check engine light goes out for the next 5-10 miles, and then comes back on. On one occasion, it went out with 1/2 tank of fuel for a few miles, and then back on again. Prior this encounter with my car, I had never even heard of a KS.

What I cannot understand is: If the KS is bad, would it not be bad at all times? If it is bad, wouldn't the check engine light remain on at all times? Since the check engine light goes OFF occasionally, could the KS be good, with some other issue causing the code to be thrown?

I hate the thought of having to replace KS's in that they are quite costly, only to find out that some other issue is causing the KS code. Although the engine runs smoothly (and quietly), if the timing is advanced/retarded, could this cause the code?

So, I do not know what to do, or not to do. Any suggestions, help and/or advice will be greatly appreciated. Thank you.

 

When the knock sensor code lit up for me, it was of an on for a wile. I even passed state inspection while it was off and as I drove out it came on. At about 150k miles the sensors seem to go bad. Premium fuel seems to keep the light off a bit longer. I started carrying the obdII reader to clear the code to get the o/d.

The solution was to replace both sensors. Read the DIY and order the harness as well.

Salim

 

I had to replace one knock sensor I ordered it off amazon for $60ish and had a local shop to do it in an hour for like $80. Saved a lot by not going to a dealer.

 

The dealer would bill you based on book-hours and their labor rate. Since I did those myself I cant imagine any one doing it in less than 3hours [it took me about 8 ,,,, you can see the DIY] and I think the book-hours are somewhere between 5 and 6.

Maybe there is a short-cut we all need to learn.

You made the right decision to replace one, but if the labor is say 6hrs, then one should replace both.


Salim

 

Disregard that I just remembered that was the O2 sensor.

 

Thank you to all who replied. Today the light went out again. I have put about 50 miles on the vehicle, and it has not returned...YET. I am still interested to learn what can trigger the computer to trip the KS code. If the KS come on and goes off without resetting the computer, it would seem that the KS itself is good and that something is happening that activates the code and causes the check engine light to come on. Stated another way, if the KS itself is bad, can it cause the check engine light to randomly come on and go off. Just seems that the part would either be functioning properly, or not functioning at all. I would assume that the KS is designed to warn of a potential knocking problem. Could there be an issue with some other part or parts that is causing the KS to do its job? This thing is driving me nuts. Again, thanks for the input, and I await to hear more.
Thanks

 

I was in the same boat. For my case the sensor was on the verge of going bad (I could not tell of knocking). The fix for me was to replace the sensors and the harness. I can not say for sure your problem is the same as mine, but the symptoms are identical. I lived with it for about 3 months and finally took advantage of a warm day during winter time.

Detail about codes: Computer keeps collecting new codes and in case of a fault creates a pending code (pending codes can be red by the reader but do not trigger a CEL. Once certain number of pending codes accumulate, that triggers a CEL. If during the pending code time, enough good readings come in the pending codes get discarded. If enough good readings are stored the CEL goes away. The reader does allow the pending and triggered codes can reset it. Once you do the instant clear, the memory is erased and the scanner tells you channel not ready --> not enough history is there .... this when the inspection stations tell you do drive around for few days.



Salim

 

Legalease, I had the same issue come up on my 01 RX about 6 months ago at 200k. The CEL actually went off for several days one time, then came back. Since I don't have the tools or location to do it myself, I took it to a local shop that specializes in Toyota/Lexus. They checked the KS and found it to be ok, but the harness was bad. I went ahead and had them change both KS and the harnesses since they were aleady there. I didn't want to have another one go bad later and have to spend more labor $ to fix it the next time. I plan to keep the RX, so it was preventative.

 

Same thing for mine except my code started popping at around 115K. My symptoms appear similar to salimshah's. Read back in some of my earlier posts and you'll see what all I did. Toyota dealership did it for a great price. I got all the parts online. I also had the harness and a coolant hose replaced while they were in there.

 

Thanks again to all that replied. It seems that the prevailing consensus is, that the KS's begin to fail after 100,000 miles. I still cannot reconcile how the KS can be bad if the CEL repeatedly comes on and then off.
I have ordered 2 KS's, wiring harness, water intake hose, valve cover gaskets, thermostat, and seals and gaskets. I hope to have the parts delivered and the repairs completed by next weekend. I will report the outcome as soon as this occurs. Should anyone have any additional information, idea's etc. I would welcome your insight.
Best regards,
Bob

 

Your call on some of the stuff, but I would have suggested to not replace the bypass-hose and thermostat ... unless there is a problem with it. Coolant drain and fill is the right call. Clean the IACV while you are at it.

I would suggest read the DIY (it was put together by input from lots of folks ... the knowledge in the thread can be useful, even if you have some one else do the job.

Good luck.

Salim

 

My knock sensors are still original at 174k miles. I wonder why some die earlier than others... I always fill up 93 octane, that may be one of the reasons mine is still alive. lol

 

Had to replace my knock sensors at 120k.

 

Update: This past weekend I replaced both knock sensors, water hose, and wiring harness. While I was in this far, I also replaced the spark plugs (Denso) and the thermostat. Since doing so I have put about 150 miles on the vehicle, and all seems fine. The dreaded CEL has not reappeared. Fingers are still crossed. Again, thanks for the advise. It is greatly appreciated.
Bob

 

Thanks for the update.

I think you have solved the issue.

Did you do it yourself or paid for it?

Salim