Knock sensor woes - need advice

[J A Blazer]

Pardon the long post but I need advice. 2000 4 cyl. OBW, AT, 158K. Purchased 6 years ago from original owner, w/ 85K. In recent years the check engine light came on often enough that I bought a cheap code reader. Codes were 328 and 420. New pre-cat O2 sensor, fix exhaust leak, and reattach heat shield have hopefully put the 420 to rest.

 

In August 2011 I broke down and bought a new OE O2 sensor. Went to install it but sensed some possible cross-threading in the original location, so I placed it in the 'other' spot, a few inches back and to the right. Didn't really end the problem, but may have reduced the frequency.

 

Monday of this week I took the car to the dealer for some unrelated work that I couldn't do myself. On the way to the dealer the CEL came on. Scanned the code and sure enough a 328. Asked the dealer to investigate. They insisted on selling me a new knock sensor, chasing the original threads, and placing the new sensor 'where it belongs.' I wasn't happy, but agreed. They cleared the codes. Picked the car up the next day, and 5 miles later the CEL back on; sure enough, a 328. I called the dealer, expressing my displeasure (to put it mildly.) We agreed that I would not clear the codes and would return to the dealer in a few days (a part for an unrelated repair had to be ordered.)

 

Anyways, the next day the CEL spontaneously went out. Then a day or so later it came back on. I scanned it, still a 328. Then it went out again, and that is the present state of affairs, although a scan still reveals P0328.

 

What's going on here? Under these circumstances is there some sort of 'learning curve' once new sensors are installed, even though the codes have been cleared? A search of various sites, both Subaru-specific and generic, suggests that worn engine mounts may be a possible cause of a knock sensor code.

 

The collective wisdom of the group would be greatly appreciated. I plan on driving the car a lot this weekend before taking it back to the dealer on Monday.

Edited September 21, 2012 by J A Blazer
typo

[nipper]

NO learning curve.

 

I would inspect the connector itself, make sure it is clean and a firm connection.

 

And it is possible for new barts to be bad, it happens.

[Fairtax4me]

P0328 knock sensor circuit High input

Per MY2000 FSM.

Dtc detecting condition: immediately at fault recognition.

 

Check harness between KS and ECU connector. Connector B136 Pin 4. Check resistance is less than 400k ohm. If yes then, Check resistance of knock sensor, less than 400k ohm. If no check input voltage at ECU, more than 2v.

Knock sensor resistance less than 400k ohm, bad knock sensor. 400k ohm or more, bad ground or bad connection between ECU and knock sensor.

ECM input voltage less than2v, poor connection between knock sensor and ECU. With a brand new OE sensor I would certainly blame a poor connection before the sensor but it's entirely possible the sensor is bad.

If the block surface under the sensor is corroded that can cause issues as well.

[J A Blazer]

Where do I find ECU connector B136?

[Cougar]

Connector B136 is one of the three connectors that tie to the ECU, which is mounted under the dash. It is a 30 pin connector and should be the one closest to the passenger area.

[idosubaru]

two very talented jokers are posting replies to your thread - follow along closely, follow their suggestions, and answer their questions.