knock sensor (P0325) questions

hi all, I took 97 wagon out for a drive today and the CEL went off. When I got home I hooked up my obd2 scanner and pulled a p0325 code, knock sensor. So I was planning to pull it and check to see if it needs replacing, but in the event that the knock sensor is properly detecting something, what are the common causes or problems that would lead to setting off the knock sensor?

 

a little info on my wagon, again its a 97 2.5gt, I just recently bought it and I've been in the middle of a full tune up. So far I flushed the radiator, changed the oil, air filter, changed the rear diff fluid, switched the radio out and did some minor body work. I still need to change the plugs, wires, and fuel filter. It still runs a bit rough, and I'm also contemplating upgrading to an msd coil.

 

any help or info would be really appreciated. Happy new years!

When my 97 Legacy threw a knock sensor code, I pulled it and found a hairline crack on it, replaced it and that problem was solved. I also found a hairline crack in one of the coil on plug, had to order them from China, I hope that will solve my rough idle problem.. Knock sensor should be listening for misfires caused by any fault in the combustion process. Although a misfire should show up us a separate fault code.

thanks for the input, that's a great point. If the sensor was correctly detecting some sort of misfire there should be some other codes being tripped. I'm going to replace this sensor and see if that does the trick.

You can get an eBay knock sensor for $10.

do you know if that eBay sensor is reliable at all? So far I've only been able to find that thing for about 80 bucks

I've used two of them. One on each of my subies. So far they have held up for about a year. They appear the same and were spot on spec when I tested them with my multimeter.

thanks for the input. I'll be ordering one this week. Do you know off hand what the torque spec is on that bolt in the center?

It's 12-14 ft. lbs. Might be a good idea to reset your ecu by disconnecting the battery for 20-40 minutes. My cel went away without doing this though.

I got an obd scanner for resets but yeah, I'll be disconnecting the Bart for good measure once I get this done.

My knock sensor exhibited intermittent hard start problems for a while, eventually a no start. I had no codes set. After describing the symptoms to a tech he quickly said knock sensor. $26. No visual signs inspecting old part. I was told it was not un-common.

hate to res an old thread, but better than starting a new one. Would a bad knock sensor cause a huge drop in gas mileage? I'm assuming it is putting the car in "limp mode" because I went from 21-22 MPG down to 15. The light had came on previously and I reset it, and it seemed to drive normally after that. The only thing that caused the light to come back on was climbing a big hill.

 

Also, do we have multiple knock sensors? I've never done one on a 2nd gen. I've done multiple on the 1rst gen legacies though, I'm assuming it is in the same spot, under the intake elbow on the engine block, is this the correct part to buy? Engine code is 325 as well

 

http://www.ebay.com/itm/B864-Subaru-Legacy-Impreza-Forester-2-5-Knock-Sensor-96-97-98-99-New-/110801453412?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1999%7CModel%3ALegacy%7CSubmodel%3AGT&hash=item19cc480164&vxp=mtr

hate to res an old thread, but better than starting a new one. Would a bad knock sensor cause a huge drop in gas mileage? I'm assuming it is putting the car in "limp mode" because I went from 21-22 MPG down to 15. The light had came on previously and I reset it, and it seemed to drive normally after that. The only thing that caused the light to come back on was climbing a big hill.

 

Also, do we have multiple knock sensors? I've never done one on a 2nd gen. I've done multiple on the 1rst gen legacies though, I'm assuming it is in the same spot, under the intake elbow on the engine block, is this the correct part to buy? Engine code is 325 as well

 

http://www.ebay.com/itm/B864-Subaru-Legacy-Impreza-Forester-2-5-Knock-Sensor-96-97-98-99-New-/110801453412?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1999%7CModel%3ALegacy%7CSubmodel%3AGT&hash=item19cc480164&vxp=mtr

 

Yes. It will also cause the car to become very sluggish, much like what happens when you get a bad O2 sensor.

 

No, we only have 1 knock sensor & it's in the same exact spot as the first gens. Buy the $10 piece from eBay. I purchased one a while back & haven't had a problem since.

Additional info (may or may not apply):

 

http://www.northursalia.com/techdocs/pdf/engine/knock.pdf

Well, I have an hour and half drive (each way) tomorrow all freeway. So I took out my stock knock sensor to check on it. The plastic does have a small crack in it, so all i could really do was clean the mating surface and put it on. Pretty sure I stripped out the threads on the block though

Not sure how, the bolt looked fine but I just couldn't get the threads to start, so I finally got them started and it was a little resistive so I figured there might been gunk in the threads or something. I got it torqued down at 20 ft lbs. Hopefully they aren't stripped out, or at least the knock sensor is still mounted flush. Anyways I went to get some gas (figured I'd try premium) and the CEL didn't come on, even when getting on it a bit. I guess I'll see how it goes tomorrow. Damn ebay sensor should be here soon but never soon enough. Oh well, i saved $72 so can't complain

My solution for stripped threads; I mix up a small portion of JB weld, fill the stripped out hole,(very light) coat of anti-seize on the bolt, screw the bolt in, wait 15 minutes for the JB-weld to partly cure, unscrew the bolt a few times, wait uvernight for complete cure, install my part and torque down to spec. It worked for me not sure how it work for anyone else.

I use a drill bit an retap the hole. Lots of lubricant, Liquid Wrench works nicely. Trick is to take your time and tap the new hole slowly, lubricating it often and reversing it periodically.

Agreed, industry standards VS Mcgyver in a pinch.