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Knock Sensor replacement


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18 replies to this topic

#1 Peter Parker

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Posted 03 May 2005 - 06:02 PM

Hello all,
New to this board. I have a 99 Outback Legacy with 98,000 miles. My check engine light came on a while back and I went to the local repair shop to read the codes. They said the knock sensor is failing. So I ordered a new sensor and it is on the way. My cheapy shop manual has terrible instructions and an even worse photo of the sensor on the engine.

I was wondering if someone out there might have some helpful advice and possibly a detailed photo depicting the exact location of the sensor?

Thanks in advance.

Peter

#2 Cougar

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Posted 03 May 2005 - 06:49 PM

Welcome to the board Spiderman.

I think the sensor can be found on top of the engine towards the rear end.

#3 royboy159

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Posted 03 May 2005 - 07:09 PM

Hey Peter---I knew Spiderman drove a Soob!:grin:
Just a tip. Get the exact torque spec for the new sensor. It can make a difference.

#4 hklaine

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Posted 03 May 2005 - 09:24 PM

I stole this from somewhere a while back. Credit to whoever put it together.
If you have EJ25 maybe its similar - (?)



Some quick notes and pictures on how to replace the knock sensor on a 1995 Subaru Legacy Outback (2.2 liter EJ22 engine).

Click images to enlarge.

The engine - not very clean!
Posted Image

New knock sensor.
Posted Image

Move the throttle body intake pipe out of the way.
Posted Image

Sensor location is on the driver's side rear close to the throttle body. Arrow points to it.
Posted Image Posted Image

Remove the sensor with an extension and 12mm socket.
Posted Image

Old sensor removed.
Posted Image

Install the new sensor. Torque the bolt to 16ft-lbs.
Posted Image

Clear the engine code (if present) using some sort of OBD scan-tool.

#5 grossgary

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Posted 03 May 2005 - 10:53 PM

check the wiring to the sensor. a dirty connector/harness or exposed wire can cause the knock sensor code in the ECU as well.

#6 Peter Parker

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Posted 04 May 2005 - 10:38 AM

Thanks, this is just what I was looking for! Hope the 2.5 is similar.


I stole this from somewhere a while back. Credit to whoever put it together.
If you have EJ25 maybe its similar - (?)



Some quick notes and pictures on how to replace the knock sensor on a 1995 Subaru Legacy Outback (2.2 liter EJ22 engine).

Click images to enlarge.

The engine - not very clean!
Posted Image

New knock sensor.
Posted Image

Move the throttle body intake pipe out of the way.
Posted Image

Sensor location is on the driver's side rear close to the throttle body. Arrow points to it.
Posted Image Posted Image

Remove the sensor with an extension and 12mm socket.
Posted Image

Old sensor removed.
Posted Image

Install the new sensor. Torque the bolt to 16ft-lbs.
Posted Image

Clear the engine code (if present) using some sort of OBD scan-tool.



#7 Peter Parker

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Posted 04 May 2005 - 10:40 AM

I figured this could have been the problem too, but I didn't know where to find the sensor. I will try this before replacing the sensor.
Thanks for the information!.

check the wiring to the sensor. a dirty connector/harness or exposed wire can cause the knock sensor code in the ECU as well.



#8 ddddc

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Posted 27 July 2005 - 07:40 AM

I have the same problem with my 1998GT. The knock sensor on the 2.5L appears to be tough to get to and not an easy job to change out or test. My Haynes manual indicates that quite a bit of the top of the engine needs to be removed, which includes the alternator and manifold assembly. Is there an easy/quick way to remove this sensor, one that doesn't require major disassembly? Thanks in advance.

#9 rcoaster

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Posted 27 July 2005 - 07:48 AM

I have the same problem with my 1998GT. The knock sensor on the 2.5L appears to be tough to get to and not an easy job to change out or test. My Haynes manual indicates that quite a bit of the top of the engine needs to be removed, which includes the alternator and manifold assembly. Is there an easy/quick way to remove this sensor, one that doesn't require major disassembly? Thanks in advance.


Also, it mentions about draining some of the coolant out since the bolt extends into the cooling passages. Is this true?

#10 hawksoob

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Posted 27 July 2005 - 08:54 AM

Also, it mentions about draining some of the coolant out since the bolt extends into the cooling passages. Is this true?


For sure on a 2.2, no ... draining of coolant is not necessary. Neither is removing the intake manifold as the Haynes says. Going by Haynes, this would be a one hour job. Going by reality, it's less than 5 minutes.

#11 subyrally

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Posted 27 July 2005 - 09:55 AM

in the sohc ej25, you only need a long socket extention and i think a 12or 14mm socket.i replaced mine a couple years ago, in the walmart parking lot after i bought my first set of tools. well, not my first set of tool, but it was like the first set of high quality sockets and extentions. the hardest part of the replacement was getting the sensor hooked up to the harness if i remember correctly.

#12 Peter Parker

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Posted 27 July 2005 - 11:00 AM

Thank you for the information. After I posted the original question, I did replace the sensor and the engine check light is now off. I did have to remove the air cleaner components. Getting the bolt down through the sensor was a bit tricky with all the other stuff in the way. In all about a half hours work.
Cheers!

#13 Cougar

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Posted 27 July 2005 - 11:54 AM

Glad you got it fixed. Now you can get on with the more important duties of a superhero.

#14 Peter Parker

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Posted 27 July 2005 - 02:16 PM

Thats right... every super hero needs a trustworthy vehicle! :rolleyes:

#15 royboy159

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Posted 27 July 2005 - 04:49 PM

Thank you for the information. After I posted the original question, I did replace the sensor and the engine check light is now off. I did have to remove the air cleaner components. Getting the bolt down through the sensor was a bit tricky with all the other stuff in the way. In all about a half hours work.
Cheers!

Hey Peter----Good to see this update. So many threads just die. The good ones keep coming back to life.:banana:

#16 ddddc

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Posted 29 July 2005 - 06:22 PM

Mission accomplished based on the photos and post comments! Thanks everyone. It was a quick job like everyone mentioned on the 2.5L in my 1998 Legacy GT. Having a magnet tool helped in retrieving the bolt. My check-engine light is off and the car's power band seems to have returned. Still not as much power or quickness as a friends 1997 Legacy Outback (maybe the GT's weighs more than the outback, both are 5 spds?)

#17 MorganM

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Posted 26 September 2008 - 08:28 AM

This was a helpful " how to " for changing a knock sensor. With out that graphic I wouldn't have known exactly how to position the sensor.

#18 JT95

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Posted 29 September 2008 - 10:38 PM

For sure on a 2.2, no ... draining of coolant is not necessary. Neither is removing the intake manifold as the Haynes says. Going by Haynes, this would be a one hour job. Going by reality, it's less than 5 minutes.



He is right on. My 95 LSi wagon threw that code. I got a knock sensor from O'Reiley's for way cheaper than anyone else. The manual said to do all this stuff, I looked under the hood, then swapped them out without removing a thing. Some graceful fingering is involved, but be patient and save yourself all that hassle of going all out. I unplugged the battery to reset the ECU, and was good to go.

#19 MorganM

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Posted 30 September 2008 - 09:09 AM

For me I had to unplug the cam position sensor, the two fuel injectors on the drivers side, and some little red purge solenoid or something. Then I could pull the wire harness that was in the way so that I had enough room to work on the knock sensor. That was really the only thing in my way. This was an EJ22.




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