SimonBones 1 #1 July 8, 2009 Hey out there! For anyone experienced in Subaru vehicles may I pick your brain? I recently got the Check Engine light in my 2001 Subaru Outback. I read the code and got two of them: P0328 - Knock sensor circuit high input P0420 - Catalyst System Efficiency Below Threshold I'm not familiar with a Knock circuit but know it has something to do with ignition. I also know that the cat converter codes can go on an ignition problem. I'm weary to take this to a mechanic shop (since I haven't found a good one yet) and know they'll just try and get me to buy a whole new cat converter. Thoughts?108 way head down world record!!! http://www.simonbones.com Hit me up on Facebook Quote Share this post Link to post Share on other sites
theonlyski 3 #2 July 8, 2009 The knock sensor is a sensor thats usually found on the block of the engine to detect detonation in your cylinders so that it can adjust your mixture."I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly DPH -7, TDS 578, Muff 5153, SCR 14890 I'm an asshole, and I approve this message Quote Share this post Link to post Share on other sites
SimonBones 1 #3 July 8, 2009 So then the two codes should definitely be related symptoms of one problem right? I know that cat converter codes can trip on a mixture problem too. Any ideas for a good first place to look?108 way head down world record!!! http://www.simonbones.com Hit me up on Facebook Quote Share this post Link to post Share on other sites
theonlyski 3 #4 July 8, 2009 It would make sense that the knock sensor is acting up and not allowing enough, or allowing too much fuel into the system, causing the O2 sensor to read out of tollerance. To me atleast... I would see whats up with the knock sensor first, they're alot cheaper IIRC."I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly DPH -7, TDS 578, Muff 5153, SCR 14890 I'm an asshole, and I approve this message Quote Share this post Link to post Share on other sites
DavidB 0 #5 July 8, 2009 QuoteThe knock sensor is a sensor thats usually found on the block of the engine to detect detonation in your cylinders so that it can adjust your mixture. Actually it will adjust the timing, & if a high input situation would retard timing (make it think it's knocking) then yes I could very easily see that dropping your overall MPG, losing some power, & overheating/melting the converter. The problem is, you don't know if the knock sensor is bad or something up-stream of it, & without a service manual all you can do is throw parts at it. Even with a service manual these things can be really difficult to diagnose & trace. The service manual for my 68 Dart is 8-1/2X11 & 1.5" thick. The electrical diagrams in the service manual for my 94 F-150 is twice the thickness of my Dart manual, and that's only the engine management! The body electrical is another volume the size of my Dart manual (which BTW covers Dart, Coronet, & Charger), then the mechanical volumes (2) & you end up with literally thousands of pages of confusion. Yes, it can be overwhelming at times.When the only tool you have is a hammer, every problem looks like a nail. Quote Share this post Link to post Share on other sites
jonstark 8 #6 July 9, 2009 QuoteHey out there! For anyone experienced in Subaru vehicles may I pick your brain? I recently got the Check Engine light in my 2001 Subaru Outback. I read the code and got two of them: P0328 - Knock sensor circuit high input P0420 - Catalyst System Efficiency Below Threshold I'm not familiar with a Knock circuit but know it has something to do with ignition. I also know that the cat converter codes can go on an ignition problem. I'm weary to take this to a mechanic shop (since I haven't found a good one yet) and know they'll just try and get me to buy a whole new cat converter. Thoughts? Simply get it onto an analyzer and find out whether a knock sensor has failed. If so this would make the fuel timing different from normal causing the catalytic fault due to a rich mixture trying to cool the engine to prevent knocking or detonation. Did you change fuel types lately? Get a bad batch of gas? That'll do it too. jon Quote Share this post Link to post Share on other sites
SimonBones 1 #7 July 15, 2009 So... little update here (I forgot about this thread), I figured I should test my knock sensor to see if there is anything wrong with it. Disconnected it from the ECM and did some resistance readings. Well over a MegaOhm in resistance to ground. On the ECM side, over 450K Ohms to ground. Definitely not grounded. Checked the voltage input from the ECM. About 4.8 volts, no problem there. Everything I checked about the sensor was looking good. Considering that all the other repairs would be much more costly, I went out and bought a new one for $80 and took out the old knock sensor. Resistance measurements from terminal to sensor area were exactly the same from the old one to the new one. Everything measurement I could think of between the new and old sensors were the same. I put in the new one anyway and left my negative battery terminal unplugged for a while. The next morning I went out and drove over 40 miles on and off highways and the check engine light did not come back on. So I guess that fixed it. I'm still confused though how every measurement between the two came out the same, they looked the same, no visible damage on the old one, yet the old one was tripping two error codes and the new one worked great. Oh well, I guess I'm just not smart enough!108 way head down world record!!! http://www.simonbones.com Hit me up on Facebook Quote Share this post Link to post Share on other sites
