Autozone checked my CEL for me and the code is a malfunctioning knock sensor. I have a 96 Subaru AWD Legacy. Anyone changed one? Is it a DIY or should I take it to the shop?

 

Glenn

Real easy to DIY. It's right on top of the engine, on the driver's side behind/under the intake manifold. Just need a ratchet and about 12" extension.

Car has been running fine. Should I be concerned that is a sign of a bigger problem or just a sensor acting up?

Busted knock sensors don't make the car run any differently. Mine was broke for years before I got a new one and it didn't affect MPG at all.

 

It's a very easy fix, just attack it from the left side of the engine and use a 12 or 8" extension.

Since it's been running good, reset the code and give it a week or two. It may not come back. Sometimes codes set just because they feel like it.

I had a code for the malfunctioning knock sensor on my 95 Legacy L "Outback" 2.2L a couple of months back. It took me a while to replace it and I def. noticed less power with it malfunctioning. With no knock sensor the engine computer goes into a failsafe mode doesn't apply any spark advance to prevent knocking.

 

Changing it was pretty easy, the Haynes manual describes removing the intake manifold but its not necessary. Like the previous poster said, the right sized socket extension and it comes out pretty easily, work with the engine completely cool as you have to snake your hand down under the throttle body to unplug/plug in the sensor and start the bolt in the block.

you'll also need a torque wrench ...if your going to do it the right way...i forget what the torque is but if u search you'll find it

If you washed the engine compartment or ran thru a big puddle that might be why it came on.

 

They do fail regularly.

 

They affect ALOT more than people think, as stated above they retard/advance timing, which does mess with fuel mix, etc.

 

Probably around $100 for a new one from the dealer if I had to guess but you could try used ones from a pull a part yard, probably pull 5 in under 30 minutes.

 

Unplug it with a small flat screwdriver, then Sneak a 12" extension behind the throttle cable attachments and unbolt it from the engine. If you dont have a torque wrench a 3/8" 6" long ratchet with a 12" extension should give you about the right torque.

From the FSM:

 

1) Install knock sensor to cylinder block.

 

Tightening torque:

23.5± 2.9 N·m (2.4± 0.3 kg-m, 17.4± 2.2 ft-lb)

 

NOTE:

The extraction area of the knock sensor cord must be positioned at a 45° angle relative to the engine rear.

 

2) Connect knock sensor connector.

3) Install air cleaner case.

 

Translation: I guess the "extraction area of the knock sensor cord" means the connector. See picture.

The single bolt that holds it in place takes a 12mm socket, and goes through the center of the sensor.

i only paid like 60 for mine....i got it through 1stsubaruparts.com or something like that

I started getting the knock sensor malf. code about every 1,000 miles or so after clearing the code. A few thousand miles past that and it started to stay on, the light only going off every once in a while. By that time my mileage had decreased from 29-30 mpg highway to about 24-25. I also noticed a distinct miss, sometimes at half-throttle, sometimes at full throttle. Always when the a/c was on. After about 30,000 miles w/ a knock sensor code, I finally replaced it. Man the difference was night and day! You can definitely feel it retard the timing a few seconds before that light comes on.

when my knock sensor went bad it sometimes ran rough or stalled, and sounded strange when decellerating. got the new one at Autozone in Carlisle for $44. 6000 miles later no problem.