# Knock sensor **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [March 22, 2008, 8:35pm UTC](https://community.cartalk.com/t/knock-sensor/12088 "2008-03-22T20:35:38Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![unionave](https://avatars.discourse-cdn.com/v4/letter/u/9de0a6/32.png) [@unionave](https://community.cartalk.com/u/unionave)\ **Post date:** [March 22, 2008, 8:35pm UTC](https://community.cartalk.com/t/knock-sensor/12088/1 "2008-03-22T20:35:38Z")
2002 Subaru Outback Sp. w/ 65k. Check engine light went on, took to auto zone for reading and said knock sensor replacement. How serious is this and how much $$$? Guy at auto zone said pretty common for subarus. ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [March 22, 2008, 8:52pm UTC](https://community.cartalk.com/t/knock-sensor/12088/2 "2008-03-22T20:52:06Z")
it’s normally not too serious and could only be a problem if your vehicle has a pre-ignition rattle. most pre-ignition rattles are usually caused by an EGR system fault and the knock sensor will offset this up to a point. the “up to a point” means that if a rattle is bad enough the ecm may not be able to retard the timing enough to stop the rattle. chronic, long term ign. rattles can damage an engine. no idea on costs as that depends on the part supplier, shop labor rate, etc. keep in mind that a knock sensor code does not necessarily mean the kn. sensor is bad; only that a fault exists in that circuit. it could be a loose or corroded wire connector for example. hope that helps ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [March 23, 2008, 1:08am UTC](https://community.cartalk.com/t/knock-sensor/12088/3 "2008-03-23T01:08:02Z")
The DTC (Diagnostic Trouble Code) only indicates that there is a problem in the knock sensor circuit. There are NO trouble code which say that ANY part requires replacement. There are even shops and “mechanics” who will change an (expensive) part as part of experimental troubleshooting. Try to find a shop/mechanic who, only, changes parts for verified reasons…just a code showing up is not enough reason. ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [March 23, 2008, 4:22am UTC](https://community.cartalk.com/t/knock-sensor/12088/4 "2008-03-23T04:22:23Z")
You said that you are an electrician. Are you saying that you won’t get the repair manual, look in the section for checking the sensors and actuator with your multimeter, and follow the instruction steps? How do you decide if a component is faulty if you don’t test it? ---
**Author:** ![tarmin21](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@tarmin21](https://community.cartalk.com/u/tarmin21)\ **Post date:** [June 19, 2008, 4:07pm UTC](https://community.cartalk.com/t/knock-sensor/12088/5 "2008-06-19T16:07:06Z")
Had a similar problem on my Subaru Outback 98. Check engine light gave a knock sensor code and engine idle was rough. Purchased a new sensor from AutoZone for around $90 and installed it myself. This corrected the CEL and idle. If you decide to do the repair yourself here is a helpful website [http://www.scoobymods.com/forums/showthread.php?t=4039&highlight=knock+sensor](http://www.scoobymods.com/forums/showthread.php?t=4039&highlight=knock+sensor) ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [June 19, 2008, 4:53pm UTC](https://community.cartalk.com/t/knock-sensor/12088/6 "2008-06-19T16:53:11Z")
As you see from some of the posts, some people changed a sensor, and it cured the problem. You, too, can do the “parts change experiment”. It might work It’ll only cost you $90 plus labor to find out. The Haynes repair manual gives you a test, where you rap the engine block with a hammer, that you could do. Which do you choose?