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Knock sensor


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17 replies to this topic

#1 CJK440

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Posted 01 March 2004 - 07:13 PM

I have a check engine light on my 96 Legacy GT.

It was scanned and shows a knock sensor problem. I changed plugs, undid the battery and no difference.

Should I look at the sensor itself?? Any way to test it????

Would a tank of 87 octane cause a check engine light when Subaru recomends 91 octane???

I recently filled it with 93 but after I pulled the battery cable so maybe the fuel change helped but the computer is still showing the old fault.

#2 blitz

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Posted 01 March 2004 - 07:42 PM

Measure it with an ohmeter. Normal resistance for MY'02 sensor is right about a half Meg, but I think the '96 has a slightly different part and I'm not sure what the normal reading is on that. You'd have to consult the service manual for the correct spec. Also check the connector and the lead which feeds it from the harness (for a possible open or pinch to ground condition).

#3 SevenSisters

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Posted 01 March 2004 - 08:31 PM

Low octane could certianly cause a knock, particulary under load. Try to reset the MIL and see if the recommended fuel gives the same results before you change anything.

#4 CJK440

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Posted 01 March 2004 - 09:18 PM

How do I reset it, just disconnect the battery???

#5 blackbart

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Posted 01 March 2004 - 09:56 PM

My 90 Legacy knock senser code just came up, after some time checking wires, plugs etc, I saw that my timeing belt jumped a tooth. It was getting dark, I will fix the belt tomorrow. I will let you know if that was the cause.
Frank

#6 CJK440

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Posted 01 March 2004 - 10:12 PM

I just changed the timing belt.

The light was on before I did it, I disconnected the battery and the light was on after too.

#7 hawksoob

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Posted 01 March 2004 - 10:18 PM

Well, the knock sensor IS 8 years old, if it's original equipment. Computer says it's bad, why not just go ahead and change it? If it's anything like mine (assume so, 96 Legacy) $40 and 5 or 10 minutes with a 12mm wrench and it's done.

My light came on, said bad knocker. Various times the light went away after the battery was disconnected. Came on again within 5 minutes. Swapped it, no more CEL.

#8 CJK440

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Posted 01 March 2004 - 10:26 PM

Hmm, its that easy to swap out??? I took a look through my Haynes manual to just get an idea as to the size of the job and they get into how the intake manifold needs to be removed to get at the thing.

Its a 96 Legacy GT with the 2.5L DOHC.

#9 hawksoob

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Posted 01 March 2004 - 11:09 PM

Haynes is pretty warped when it comes to the knock sensor. I had the same trepidation. "Remove intake manifold and drain the coolant?" WTF?!!!! It's way off.

Just to be sure: If it's like the 2.2L, look underneath the throttle body, just left of center of the engine (looking towards the front). A little black donut looking thing, about the size of a quarter, about an inch thick, 12mm bolt in the middle and a wire coming out. It's a matter of loosening the bolt, unhooking the connecing wire, and reversing. It was quite simple with a box wrench with a ratchet mechanisim built-in. A standard ratchet would work OK, but would bust a knuckle or two, as would a standard box wrench. It's kind of a tight fit, but very doable.

#10 hawksoob

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Posted 01 March 2004 - 11:13 PM

You can get one here:

http://catalog.thepa...&imageField.y=9

Seem to be a good organization. Got my stuff quick with no problems. If you need other stuff, go ahead and get it. Free shipping over $50.

#11 DerFahrer

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Posted 02 March 2004 - 12:37 PM

I have never seen the Haynes manual be more wrong about something. No, there is absolutely no reason to remove the intake manifold, and not one drop of coolant comes in contact with the sensor.

Just unscrew the bolt and remove the old sensor, and then put the new sensor in place and lower the bolt in place with a long magnet-reacher (you NEED to do this, unless you wanna drop the bolt down onto the block under the intake manifold, never to be seen again :eek: ) then retighten and plug it in.

1st-gen Legacies' original sensors had a grey connector to the wiring harness. These sensors are known for being oversensitive and sometimes crack. Your new sensor should come with a white connector, this one is updated and has addressed some of these issues.

#12 hawksoob

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Posted 02 March 2004 - 01:43 PM

Originally posted by subyluvr2212
I have never seen the Haynes manual be more wrong about something.



Yeah. Made me nervous to do anything else based on the Haynes before I double and treble checked here and various other refernces. I cross with Chilton's, here, NASIOC and the tech references downloaded from Subaru.

#13 myles

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Posted 02 March 2004 - 07:33 PM

Originally posted by hawksoob
Yeah. Made me nervous to do anything else based on the Haynes before I double and treble checked here and various other refernces. I cross with Chilton's, here, NASIOC and the tech references downloaded from Subaru.



Why not download the FSM's from http://techinfo.subaru.com/ for US$20? It's a bit tedious, but they're (obviously) far more accurate than the aftermarket books.

Also, tighten to the specified torque (as specified by Subaru, not Haynes :) ).

#14 hawksoob

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Posted 02 March 2004 - 07:41 PM

Originally posted by myles
Why not download the FSM's from http://techinfo.subaru.com/ for US$20?



Yeah, that's what I meant by "tech references from Subaru". Just couldn't think of the actual term at the time.

Wonderful service.

#15 CJK440

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Posted 03 March 2004 - 05:04 PM

OK, Took off old sensor, it had a white plug and the plastic body was cracked.

I bought a new sensor, installed it (easy) and light is still on.

I undid the batterey for 1 minute to clear it and nothing.

???? Maybe I have another issue.

#16 hawksoob

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Posted 03 March 2004 - 05:10 PM

Have an Autozone nearby? They check CEL codes for free.

Plus, one minute may not do it. Try unhooking the battery for 15+ minutes.

#17 Setright

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Posted 05 March 2004 - 02:51 PM

If you wanna be sure, disconnect the battery for an hour. Start the engine, dont touch anything, let it idle up to normal operating temp, and switch it off.

#18 CJK440

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Posted 06 March 2004 - 04:00 PM

I took the car to autozone. They scanned it and it showed the knock sensor code. I assume this was a residual memory code so I had the guy clear it.

Lights off and all seems good.




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