I was able to clear up the 3 misfire codes I was getting with my '99 Subaru Outback by changing spark plug wires.

 

I got a code for knock sensor.  Does this affect performance?  Thanks.

Yes. When a knock is detected, the ecu pulls timing.

Replacements are under $20 on Ebay. Just buy one from a US based  firm as it'll take 3 weeks or more otherwise.

 

O.

Yes. When a knock is detected, the ecu pulls timing.

Replacements are under $20 on Ebay. Just buy one from a US based  firm as it'll take 3 weeks or more otherwise.

 

O.

My experience when the knock sensor went bad, is that the engine computer responded by retarding the timing. The engine then had about 50 less horse power, and gas millage was poor. When a knock sensor fails that bad, you cannot fail to realize that something is very wrong.

I was able to clear up the 3 misfire codes I was getting with my '99 Subaru Outback by changing spark plug wires.

 

I got a code for knock sensor.  Does this affect performance?  Thanks.

 

Absolutely the knock sensor can hurt performance and mileage... in fact they can even be flaky enough to affect performance BEFORE they trip an ECU code. In case you don't have any experience with these sensors I made a video when I changed one of mine out a couple years ago that might help give you some familiarity with the process...:

 

OK, thanks for the information.  I am noticing no performance issues so maybe the Auto Zone guy got the code wrong?

 

Absolutely the knock sensor can hurt performance and mileage... in fact they can even be flaky enough to affect performance BEFORE they trip an ECU code. In case you don't have any experience with these sensors I made a video when I changed one of mine out a couple years ago that might help give you some familiarity with the process...:

 

 

Thanks for the video, it isn't that difficult a job, but there are some curve balls here; having all the tools including an extra long extender for the ratchet wrench; a magnet extender to retrieve metal objects, like screws; removal of the throttle body cover for access; potential issues with pulling the plug out; putting all the connectors back on the throttle body.  Not an easy job for non-mechanics but doable.  

Haven't watched the video, but all you really need is the 10-12 in socket extension. A swivel joint would help, but not mandatory.

The only thing you should need to remove is the airbox period. Anybody that works on cars needs a magnetic pickup. Just note the angle of the cord and replace similarly.

 

O.

+1 for a Magnetic Pickup tool.

And also for a small extendible Mirror.

Both are available at Dollar Stores for cheap.

I was getting knock sensor code still after the change; Auto Zone said they will guarantee the part.

Loosen bolt and rotate the cord then retighten. Generally the cord from the sensor ends up @1 o'clock position.

Obviously clear code after you rotate.The run.

 

O.

Thanks for the info.; hopefully by the end of the week this will be solved plus my tax snafu.

Did the replacement sensor come with a new harness/pigtail attached to the sensor? Or was it just a sensor?

 

If not, the harness on these are also notorious. Most replacements include a new/updated sensor-side harness.

It came with a wire and plug in.  Unfortunately the old wire plug in was hard to remove so the wire got pulled out of the connector, I put it back in as best I could with the new unit.

Dear All,

First week of being Subaru owner.  I got a great deal on a 1997 with 231K miles.

The CEL is on, and has been on for at least 4 years according to previous owner.  The code is P 0325 Knock sensor circuit

Does this mean that there is an engine knock, or that the sensor is bad? How can a mechanic tell the difference.  The head gasket was replaced at 131K (100K ago) and I don't know what else the knock sensor code is telling us. I cannot afford much, so am nervous that the car will not pass NJ inspection without major engine work.  The catalytic converter will be enough of an expense, but easy to understand.

If you can advise me on what the knock sensor code likely means, please do so.  Thanks!

It fails inspection also because of P 0420 Cat efficiency bank 1, but that is fairly straight forward.  I would like to know if it is front or rear, but probably best to go ahead and change out both.

 

Knock sensor.

By both I hope you mean O2 sensors. Do the front first, clear codes.

Bank 1 sensor 1 is the front unit, sensor 2 is the rear.

 

O.

Means the sensor is bad or there is a problem with the circuit for the sensor. Either damaged wire or the surface the sensor sits on is corroded and not grounding the sensor.

 

Lots of reasons for a P0420 code. Usually not because of the cats, but the engine will burn antifreeze when the head gaskets go bad, and that can damage the cats.

 

Read up on the P0420 first. Make sure spark plugs and wires are new. New fuel and air filter. New Subaru PCV valve, and make sure no vacuum hoses or any of the hoses that connect to the intake tube are split or broken. The knock sensor may even trigger that code if driven around for long enough with a bad sensor.

These are under $50 parts, not that hard to replace but be careful--pulling wires or couplers apart.  I did mine as the mechanic didn't have the time, and I didn't want to spend over $100 for the job.  I have gotten the code still once in a while after doing the job.