1999 Subaru Legacy GT (2.5L) - OBD P0325

Car has a hair under 150K miles on it, and has had regular maintenance done. CEL light has been intermittent on/off for the last couple months. Friday I went to get the emissions test, CEL pops on as I pull up to the test station after the light has been off for over two weeks. TEST FAILED!

I looked over all the connections (I think, it's almost impossible to see the knock sensor). Main Engine Block ground (large gauge wire that goes from near the starter on the block to the (-) battery terminal) was loose, re-tightened. Now get the P0325 every time the engine comes up to normal driving temp.

Is there something else to check, or go straight for the new Knock Sensor? What should I be prepared to take off to get to the darned thing?

Check both the circuit and sensor for continuity, voltage and ground.

Got a manual?

Good luck and keep us posted.

Well, except that my Subaru is a '99 SUS, I could have written your problem description. In summary, Legacy SUS 2.5L, 143K miles, Whenever the car gets warmed up, the CEL comes on. Code P0325. No knocking decernable. If car is not run for 24 hours, the CEL is out when it starts up.

Went to have Emissions Certification for licence renewal on Friday. CEL was off when I started out, but instuctions are to run for at least 20 minutes before the test to get a pass. After 15 minutes running, the CEL came on. The presence of the P0325 code in itself halted the Emissions test before it began.

Apparently the P0325 code doesn't indicate that the engine is knocking, but that the sensor output is not within the expected values. I can sometimes feel a difference in the way the car runs when the light is out versus when it is on. It runs sluggish on hills with the CEL on. What I have read indicates that when the P0325 code is present, the computer retards the timing and enriches the fuel mix. Apparently this is because it cannot detect when the car is knocking and goes into failsafe mode. This probably also explains the reduced gas milage I have had recently.

The sensor is located on the top of the engine. If you look directly below the throttle cable assembly, it is about 6 inches down sitting on the top of the block like a rubber covered donut on a string with a bolt through it.

My mechanic will be working on it tomorrow and I will let you know what he finds. Please pass along what you do to solve your problem. Good luck.

Thanks for the input, folks! I experience the same "drive-ability" behavior in mine when the light is on. [A dog @ real low RPM, and then its like I flipped the airflow myself and off she goes..., sometimes a slight gasoline odor, but not too bad, on a warm engine.] I never sense/hear what would be considered "knocking" either, and it is amazing that the code clears itself in the ~24 timespan, like yours! Sounds like they were both built the same Monday!!!!!!

I don't have a manual, but was planning to go to ALLDATAdiy.com or another online for some more help/online manual. (Better suggestion - the subscriptions are a bit expensive for a one time fix..)

I do have a Haynes for the car, but it's not real detailed. I was hoping not to have to take off the entire intake system to work on this.....I poke at it a bit more when it's cool. I do have a OBDII tester, which has proved INVALUABLE for the two Subaru's we currently own. Best $99 w/ free shipping ever, hands down!

I reset the code this morning and drove ~12 miles. It popped back on at that point (and that was within minutes of the car getting to normal operating temp). I am sort of believing the "ECU runs home to momma" idea a bit, if it gets a poor sensor feedback.

Car is cooling and I'm going to pull the harnesses and check ELEX tonight. I'll put wha I find back.

Thanks again to all for their insight. Your time here helping out is appreciated!

I, too, have that code on my 1998 Subaru Legacy with 217k miles. See my recent post. I have cleared the code and it has not returned in over a week. I did put in higher octane gas, but I'm not sure if this made any difference.

The sensor looks a bit tricky to get to buried beneath a mess of wires and plumbing. Also, it goes for about $80, so I'm hesitant to replace it until I know it's really bad.

Let me know how you make out.

Doug

Well, I got mine back this evening. The mechanic said that the specs on the sensor were for impedance of approx 7-8K ohms. Mine was in the teens when cold, but was pegging his meter over 20K ohms when it got warmed up. This may explain why the problem was intermittant.

He changed the sensor, replaced my spark plugs that had been in for 75K miles, and it is running great.

Good Luck. I will go for my emissions certification tomorrow.

It took longer to get the computer to ready all of the sensors than I expected, but once that was done, passing the certification was routine.

Hope all goes as well with yours.

Finally got back to the car. I followed the diagnostic procedure, but started by checking continuity from the harness connector on the sensor to the block. Circuit was open! Replaced the sensor, cleared the code, and it's been great ever since (have put over 100 miles on, no CEL!). Going to emissions for my retest this afternoon.

After closer inspection of the faulty sensor, it turns out there was a break in the wire about 1.5 cm down from the harness connector. The insulation was brittle so I suspect heat may have been an issue here. The sensor tested a bit higher than the new one, but still in spec.

Thanks to all for their guidance!

BTW - Getting to this on the 2.5L engine is not that bad. The most difficult part is finding it!

It's a 12mm, straight down between the intake and the throttle cables. (I had to take the pressure sprayer (CAREFULLY!) to it top be able to see the head of the bolt). There was one zip tie to cut and later replace. Really pretty easy overall.......

CEL light is now off, but I logged a "No-Test", due to not enough checks by the computer being valid.

Question of the day is "How far must I drive to log a "Full Driving Cycle" on this vehicle"?

Didn't find anything in the manuals I have, or the online subscription to the service and operation manuals.

Is it just miles, or what? Clues, anybody........

Thanks!!!!!

I can't give you a definitive answer, but I did 4 trips totaling less than 50 miles, and the test passed.

I drove home about 10 miles on the highway when I picked my car up. (I don't know how far the mechanic drove it before I got it back however) Then the next morning, ran some country roads for about 15 miles. The first test indicated that all of the sensors had not initialized. I was told that a mix of Stop and Go and highway driving was necessary to get all of the sensors ready.

I then took a 3 mile trip through some traffic lights and stopped for about 1/2 hour. Then 12 miles on the highway round about back to the test center. At that point, it passed.

Hope this helps. Good Luck!!