I've got a 1997 Subaru Impreza GC with an EJ20 (naturally aspirated) and i bought it with a bad knock sensor. There were a couple cuts in the knock sensor wire, fixed those and checked if the knock sensor code (code 22) comes up again. It did and i bought a new sensor. I replaced the sensor, reset the ECU and i'm still having the same problem. However the check engine light only comes on when the engine is cold and i start up. When it reaches normal operating temperature, the light turns off. The sensor is also torqued to spec. I was wondering if anyone could tell me where to look next to try and fix the issue. I've pretty much tried every solution i could find but with no success. Didn't find anyone who's had the same problem having the check engine light come on when cold and turn off when warm. Any ideas what i could try next? Also sorry if my english is a bit messed up.

 

I'd say if it's doing it when it's cold then damp is getting into the knock sensor as the plastic casing on it is cracked allowing damp to form when left overnight etc then with engine heat on the sensor it dries out then light goes off

similar issue occurred when I'd mine my99 years back

When refitting new one it's worth using a wee washer same size as metal sleeve so you dont crack the casing when torquing

 

We've checked the sensors i have and none of them are cracked. I've tried multiple sensors so far and it's the exact same problem everytime and CEL gives the code 22 when the engine is cold. There's also a washer about the same size as the metal sleeve to prevent from cracking the casing. I followed a guide on how to reset the ECU on classic Impreza's, and it requires the engine to be at normal operating temperature as you do the reset. However, like i said before, the check engine light always turns off when the engine has reached normal operating temperature so basically there's no problem and as the reset requires it to be at normal operating temperature, it gives me the all clear code when i reset the ECU. The next day if i go and start the car up when it's cold, the check engine light is on and CEL gives the same 22 code everytime. Here's the link to the guide i followed; http://www.scoobypedia.co.uk/index.p...ledge/ECUReset

 

I would try resetting the ecu with the engine cold. See what happens. Maybe there is genuine knock. Try some Vpower to see if the problem changes.

 

Thanks Beastie. I was thinking of doing that before. I'll try it someday. Also i was thinking could it be a bad oxygen sensor or temp sensor? If i'm not completely wrong, there was someone who mentioned having to replace both the knock sensor and the oxygen sensor to finally fix the knock sensor problem. Just can't find the post anymore in which they talked about it.

 

You wont see the cracks in the casing, also check the loom in case there are any issues with it where its potentially rubbed through on something

The knock sensor does not throw an engine light when it sees knock.

 

That seems correct. Code 22 tells us there is a fault with the sensor or wiring of the knock sensor.

 

I've already checked the loom and like i said in my first post, there were a few cuts in the knock sensor wire which have been fixed now. The rest seems fine. And yes, it won't light up the CEL if it detects knock. I believe it changes the spark timing instead if it reads excessive knock. Correct me on that if i'm wrong.

I've got a few things i wanna try out. Like i asked/mentioned before, could it be the oxygen sensor? Or maybe even a temp sensor? I remember reading a post where someone had a similar issue but i believe the check engine light never turned off for them even when reaching normal temps. They replaced both the knock sensor and the oxygen sensor and apparently it fixed the problem they were having. Felt like a bit of a long shot as my situation with the car is a bit different, but i'm honestly ready to try it out and replace some other parts to see if it fixes the issue.

I'll be pretty busy this week, but i'll get back to you asap.

 

on a classic simply take the battery off for 20mins and it will be re-set.........