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Hi All,

The check engine light came on for my daughter's 2000 Legacy Sedan (175K). The code came back to the knock sensor. The light went out quick but the code needed to be cleared. I happened again the following day and went out again.
I changed the knock sensor 4 years ago at 135K.

Any thoughts? It seems unusual that it would go bad in such a relatively short time. What does the knock sensor do and is it bad to drive this way for a while.

Thanks in advance!

Bob K
 

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the knock sensor will advance the timing to eliminate ''engine knock''. if it does not operate correctly the computer will default the timing to a non-knocking set up. this burns WAY more fuel and decreases your power.

it could be you over torqued it, or the block is dirty underneath it, or you bought a cheap unit , or you just got the one out of 10 million that were made badly.

or none of the above.

you can buy inexpensive knock sensors on ebay for less than $15 shipped. of course they may not last but 4 years. (i'll let you know in 2 years.) but they work great when new and they only take about 30 minutes to change and you can buy 3 or 4 for what they cost at the local parts store.
 

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The knock sensor I used was Genuine Subaru and cost $75.00! I am going to get one from ebay........can't be too much worse.

Thanks!
 

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I have a 2001 Outback and recently had the knock sensor replaced. Since the repair my car has more power and generally runs much better. Anyway I am curious if the knock sensor could have been bad for a long time without tripping the check engine light? I bought this car used several years ago and have been pretty disappointed with performance. In an effort to fix the issue I replaced the spark plugs, spark-plug cable, and ignition block but never noticed a change. About a year ago I needed a new cat and at the same time I replaced all of the sensors. Last week my check engine light came on and it was the knock sensor and since replacing the same its like I have a different car. Anyway could this have been the problem all along?
 

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Knock sensors routinely fail. They generally don't fail that early though, never heard of a replaced one failing - it's usually time resulting in degrading, cracked rubber that causes them to fail.

I've been using the $13-$20 ebay sensors for awhile now and so have many others across Subaru forums and issues are rare.

Given it's so easy to replace I'm seeing no need for a Subaru sensor here.
 

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Knock sensors routinely fail. They generally don't fail that early though, never heard of a replaced one failing - it's usually time resulting in degrading, cracked rubber that causes them to fail.

I've been using the $13-$20 ebay sensors for awhile now and so have many others across Subaru forums and issues are rare.

Given it's so easy to replace I'm seeing no need for a Subaru sensor here.

Ditto, generally never fail and it's the rubber that's the culprit.

Super easy to replace, likely the simplest DIY to be done.
I thought I had posted pics but I can't find it.
Anyways a new sensor is inexpensive and replacing it should resolve the error code. If you get an error code after you install the new sensor then I'd porb get a 2nd opinion - otherwise my kind of fix, cheap & quick .. good luck
 

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I have a 2001 Outback and recently had the knock sensor replaced. Since the repair my car has more power and generally runs much better. Anyway I am curious if the knock sensor could have been bad for a long time without tripping the check engine light? I bought this car used several years ago and have been pretty disappointed with performance. In an effort to fix the issue I replaced the spark plugs, spark-plug cable, and ignition block but never noticed a change. About a year ago I needed a new cat and at the same time I replaced all of the sensors. Last week my check engine light came on and it was the knock sensor and since replacing the same its like I have a different car. Anyway could this have been the problem all along?
Yes, it could.

The ECM detects a loss through the circuit and sets a code for the knock sensor. If the circuit is there, but the sensor is cracked or the casing is deteriorated, the plates will vibrate prematurely altering the resistance. When the ECM sees a knock from the knock sensor, whether its really there or not, it adds more fuel and changes the timing to balance the engine. Too much or too little fuel and timing changes make for a poor performing engine.
 
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