jlallen3rd Posted November 19, 2005 Share Posted November 19, 2005 Recently replaced the head gaskets on my 97 Legacy Outback 2.5. Shortly after I am getting a check engine light w/ a knock sensor code. Thought maybe I forgot to reconnect it but found it below the throttle body in the engine valley and it was hooked up. How do I check it? Maybe just a coincedence or could I have damaged it when I pulled the engine? Quote Link to comment Share on other sites More sharing options...
Subarunation 713 Posted November 19, 2005 Share Posted November 19, 2005 Recently replaced the head gaskets on my 97 Legacy Outback 2.5. Shortly after I am getting a check engine light w/ a knock sensor code. Thought maybe I forgot to reconnect it but found it below the throttle body in the engine valley and it was hooked up. How do I check it? Maybe just a coincedence or could I have damaged it when I pulled the engine?This sensor can be a bear. Check for any loose brackets or shields. I was getting this sensor code on a 96 OBW with 2.2. I replaced the knock sensor only to have the code come back. At long last it was an exhaust shield. I took off the shield and reset the code never to see it again. When there is a rattle the sensor MAY perceive it as a knock. When all else checks out in the ECU the ECU then decides the sensor is at fault. Clear your code and take a small hammer and tap the engine around the knock sensor a few times. See if the code comes back. One last thing, take out the sensor and clean the block and sensor very well and reassemble. See if there was dirt or corrosion between the two. After 8+ years, the knock sensor may be bad. Good luck, Greg Quote Link to comment Share on other sites More sharing options...
idosubaru Posted November 19, 2005 Share Posted November 19, 2005 check the wiring and/or connector. pull it off (i know it's a pain to get at/see) and see if you see any corrosion on the contacts. that's the starting point for many sensor issues on soobs. Quote Link to comment Share on other sites More sharing options...
jlallen3rd Posted November 19, 2005 Author Share Posted November 19, 2005 Thanx for the input. Already unhooked the connector- terminals are clean and straight. Also pulled the three connectors on the pass. side rear of block that I unhooked to remove the engine and they all look clean and straight- couldn't tell which one had the circuit for the knock sensor. Blue wire with a white trace. After clearing the code last night I went into pending codes and it reset almost immediately. This engine has had some piston slap when cold for quite awhile but it was warm when I reset. Also no noticable rattles from exhaust shields but I will check again. Is there a resistance check that can be done? I read some other posts that talk about the sensor cracking and someone putting a resistor in place until he could get a sensor. Quote Link to comment Share on other sites More sharing options...
nipper Posted November 19, 2005 Share Posted November 19, 2005 Thanx for the input. Already unhooked the connector- terminals are clean and straight. Also pulled the three connectors on the pass. side rear of block that I unhooked to remove the engine and they all look clean and straight- couldn't tell which one had the circuit for the knock sensor. Blue wire with a white trace. After clearing the code last night I went into pending codes and it reset almost immediately. This engine has had some piston slap when cold for quite awhile but it was warm when I reset. Also no noticable rattles from exhaust shields but I will check again. Is there a resistance check that can be done? I read some other posts that talk about the sensor cracking and someone putting a resistor in place until he could get a sensor. Physically inspect the sensor. The only test mentiones is to do a resistance test from the terminal to ground, it should be an open circuit. The esor has a small peice of quartz in it tha generates a AC signal, the stronger the signal the siganl the higher the knock. It may just pay to replace the sensor. nipper Quote Link to comment Share on other sites More sharing options...
subaru DR Posted November 20, 2005 Share Posted November 20, 2005 The other thing you may want to ck is to make sure the ground shielding of the wire has not poked into the sensor wire. If you have a shematic you can ck it at the ecu. I would go for the sensor first though. We have them go bad all the time. The Subaru DR Darin Recently replaced the head gaskets on my 97 Legacy Outback 2.5. Shortly after I am getting a check engine light w/ a knock sensor code. Thought maybe I forgot to reconnect it but found it below the throttle body in the engine valley and it was hooked up. How do I check it? Maybe just a coincedence or could I have damaged it when I pulled the engine? Quote Link to comment Share on other sites More sharing options...
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