Knock sensor question

[Steves72]

I have replaced the knock sensor once previously.  That last time the code was p0325.  This time the car has a p1325 code.  The cel light is not always on but it never blinks which I know is real bad for the cat.  I have no issue buying a knock sensor and installing it but I do have two questions.  Why a p1325 (now) versus a p0325 (in the past)?  While doing a search on this web site, a long time user mentioned that for $20 a knock sensor could be had on eBay.  When I did a search on eBay I found sensors for as little as $6 something and a flood of them for under $10.  I am a firm believer in you get what you pay for and $6 seems like you are buying junk.  Autozone wants $80 for one while I can pick up one from Rockauto in the 40-60 range.  Am I overthinking this?  Can I use the cheap Chinese junk being pushed on eBay or should I order the Bosch unit on Rockauto for $40?

 

Car is a 2000 Legacy Outback Limited - 173,000 miles

 

Steve

[mikaleda]

Seems like most people have good luck with the cheap chinese ones. At $6 compared to $40 I'd be willing to give it a shot, they are fairly easy to change.

[Fairtax4me]

P1325 means the reference voltage to the knock sensor is being grounded before reaching the sensor or the sensor is damaged internally and its resistance is lower than it is supposed to be.

 

If you have an ohmmeter you can test the circuit.

Use a paper clip or needle to back probe the sensor connector, turn the key On and check voltage at the connector. Should be around 2.5 volts.

Now unplug the sensor and check voltage again, voltage should be about 5 volts. If voltage is less than 4.5v, the signal wire to the sensor is probably shorted somewhere.

 

Check resistance of the knock sensor. It should be 560k-580k ohms. If resistance is higher, remove the sensor and make sure the mounting surface under the sensor is clean and free of corrosion. Re-check resistance of the sensor with it removed from the car.

 

 

If the resistance is lower than 560k ohm, the sensor is damaged and should be replaced.

[Rooster2]

A common problem is to not have a clean mating surface for the knock sensor to mate up with. Also, just a light snug when tightening is all that is needed. The knock sensor will crack and break if over tightened.

[Steves72]

Reporting back.  Temps were tolerable today so I removed the knock sensor and it appeared to be in generally good shape except for a light amount of corrosion around the edge.  I also noticed that the electrical connector was not bright and shiny.  Pulled out a brass brush and worked both the block surface and the sensor mating surface.  It was not easy to reach the electrical pin in the plug but I used a very soft emery board on it.  Put it back together and utilized a dab of dielectric grease and the code is gone.  Cost was zero but a small abrasion on the back of the hand from the throttle bracket.  Getting my hand in there to start the bolt into the block was were I got the abrasion.  Crossing my fingers and hoping that the issue is corrected.

[jfox78]

Good info. I may have to try cleaning mine as well. I have been getting the po325 code as of late.

[ThosL]

One problem I ran into was the connectors can be hard to get apart without damage; on the various price options, online orders can save $$$.  

[mikaleda]

 

One problem I ran into was the connectors can be hard to get apart without damage; on the various price options, online orders can save $$$.

A little squirt of wd40 makes a big difference when pulling any plastic connector apart. I have found most all of subarus connecters are a PITA to disconnect.

[ThosL]

Probably if the WD40 can reach in there.

[mikaleda]

 

Probably if the WD40 can reach in there.

That's what the straw is for.

[Bushwick]

Good info. I may have to try cleaning mine as well. I have been getting the po325 code as of late.

P0325 usually means it's bad. Pretty sure mine had that code and it would sometimes clear itself, then reappear. After a bunch of testing, discovered the wiring on the actual sensor itself developed an internal break where it makes a 90 degree bend up to clear the trans towards the ECM-side harness. Bending wiring cover while watching the ohmmeter verified this. Actual sensor was not cracked like most people seem to experience. I *could* have tried taping the wiring into a position that allowed for the circuit to not remain open, but that would have been a temp fix.

 

 

I went with a rockauto sensor. Chinese knock-offs (if they were purses it'd be a felony) quite often cut every corner possible. They might "work", but they aren't subjected to any quality standards, so you are definitely taking a serious risk. If it shorted internally and burned you car to the ground, not like you can sue them or even figure out WHO "them" is. 

 

A couple examples worth noting is I read how some tire molds were stolen from a Chinese factory that produced American tires. Tires were then created using the stolen molds and found their way into the US market. Tires were created using inferior rubber ingredients.  Tires failed while in use.

 

Other example is Chinese knock-offs of discontinued amplifier outputs found in older home stereo amplifiers. People dissected these and compared to dissected OEM counterparts. The knock-offs were built with thinner connections, weaker internal areas and cheaper wiring.

 

So it'snot a matter of what you pay anymore, it's a matter of IF the part was faithfully reproduced to OEM standards. When you buy the$40 part, you are getting OEM quality. When you buy the $6 part, you are technically getting an illegal knock-off that was reverse engineered and reproduced with inferior quality parts. If you bought or even sold a knock-off purse, it'd be a crime. But these electronic knock-off parts are blatantly ignored despite the potential harm being much greater than a cheaper Loius Batone purse.