My Knock Sensor Experience/Advice

[98legacy22stick]

Ever since I bought my Subaru, it has had very mild drivability problems in the lower engine RPM range such as light bucking during deceleration in gear and an occasional knock in 2nd gear under load at low RPMs. I make it sound much worse than it actually was. But having never driven a Subaru before, I attributed it to normal behavior of the car. Recently (4 years after purchasing the car), the ECU set a code P0325, for a general knock sensor circuit malfunction.

I removed the knock sensor for inspection and found that in the area where the knock sensor wire runs through the bigger loom of wires for the engine, the rubber shielding for the knock sensor wire had rubbed off and the metal shielding wire, coaxial with the knock sensor signal wire had corroded to the extent of no longer being present. The result was a poor signal being sent from the knock sensor to the ECM, resulting in less than optimal engine control (hence my drivability problems)

I replaced the knock sensor and the car runs better than ever.

I'm sharing this information because the knock sensor on the car was original, and the wire was routed just as it came from the factory. So if anyone is having some mild drivability problems without a code being thrown (took 4 years for it to get bad enough on my car) it might be worth inspecting the knock sensor and associated wiring.

[Legacy777]

Thanks for the comments. I think a few people on this board have experienced similar issues.

Subaru also updated the knock sensor design, which I'm not sure if the old design went as far forward to the 98 MY.

Glad to hear the car is running well.

[n2x4]

Subaru also updated the knock sensor design, which I'm not sure if the old design went as far forward to the 98 MY.

I don't think it did - IIRC the redesign was in 95 or 96. 98 saw the plug changeover to a 2 plug connector (with only one actually utilized).