18 replies to this topic

[robt]

So driving up a slight incline at 100kph on the primary turbo, 31 degrees and with a heavy passenger with the A/C on full I get a CEL. It just came on then went. Got home and pulled code 22 knock sensor. Quick question about how it works as I have never had a CEL come on. When there is an error does it initially flash the code (Long, long, short, short) or just do what it did on my car and come on a for a few seconds? I had music on loud so I heard no pinging. Took it really easy for the last 20 or so k's till I got home. It was fine all the way. I also thought that the knock sensor adjusted things all the time? Maybe it only detects knock in severe situations?

[RX25SE]

Normally (I don't see why a Subaru would be any different) the CEL will illuminate (not flashing) when the ECU detects a fault. The CEL will remain on while the fault is present and extinguish if the fault rectifies its self. The ECU will log the fault in its internal memory and it will remain there until cleared. Placing the ECU in diagnostic mode will cause the CEL to flash the stored code(s). First series of flashes represents the first digit of the code and the second set of flashes represents the second digit. This will be followed by a longer pause and the second code will commence (or the same code will be displayed 3 times before moving to the next code). If there is no code stored then the 'no code' code will be displayed using the same method of flashing. The knock sensor constantly monitors the engine for detonation by 'listening' to the engine. If detonation is detected by the ECU, the ECU will retard ignition timing (in a series of steps) until the knock goes away. Once knock has disappeared the ECU will begin to advance the timing until knock is again detected, and so on. This allows the engine to run with close to the maximum amount of advance. The sensor is basically a piezo crystal that generates a small voltage when it 'hears' knock. Usually if the ECU detects a fault with the knock sensor it will revert to a 'known safe' level of advance for the particular load/speed of the engine. If you are going to replace it, don't over tighten the mounting bolt (torque to specs) as this will damage the sensor. Someone may wish to confirm this is the case with a Subaru as I haven't really fiddled much with them. Hope this helps.

[robt]

Yep that helps a lot. I will clear the code and see if it comes back. I don't think I have a faulty sensor it just detonated with the heat and load. Then again I don't want to get in there to look at it with this heat.

[Alex]

How hot is it (the weather?) Also on Paul's car, he got a knock code simply because of a rattling exhaust shield. Investigate the little things like this before you start worrying.

[robt]

Its now 32 here. I think load, temp, mines chip, and A/C. Not really worried as I made it home.

[RX25SE]

I wouldn't think it will log a code just with detonation, after all that what its job is. Usually logging of a code is due to a fault with that circuit or the sensor itself. This will usually mean an 'out of range' signal being detected by the ECU. I would do just as you suggest, clear it and see if it comes back. ....or get a lighter passenger! Edit: Just saw Alex's post. Yes, a rattle or mechanical knock in the engine can trick the sensor.

[buzzda]

Normally (I don't see why a Subaru would be any different) the CEL will illuminate (not flashing) when the ECU detects a fault. The CEL will remain on while the fault is present and extinguish if the fault rectifies its self. The ECU will log the fault in its internal memory and it will remain there until cleared. Placing the ECU in diagnostic mode will cause the CEL to flash the stored code(s). First series of flashes represents the first digit of the code and the second set of flashes represents the second digit. This will be followed by a longer pause and the second code will commence (or the same code will be displayed 3 times before moving to the next code). If there is no code stored then the 'no code' code will be displayed using the same method of flashing.

The knock sensor constantly monitors the engine for detonation by 'listening' to the engine. If detonation is detected by the ECU, the ECU will retard ignition timing (in a series of steps) until the knock goes away. Once knock has disappeared the ECU will begin to advance the timing until knock is again detected, and so on. This allows the engine to run with close to the maximum amount of advance.

The sensor is basically a piezo crystal that generates a small voltage when it 'hears' knock.

Usually if the ECU detects a fault with the knock sensor it will revert to a 'known safe' level of advance for the particular load/speed of the engine.

If you are going to replace it, don't over tighten the mounting bolt (torque to specs) as this will damage the sensor.

Someone may wish to confirm this is the case with a Subaru as I haven't really fiddled much with them.

Hope this helps.

I wouldn't think it will log a code just with detonation, after all that what its job is.
Usually logging of a code is due to a fault with that circuit or the sensor itself. This will usually mean an 'out of range' signal being detected by the ECU.

I would do just as you suggest, clear it and see if it comes back.





....or get a lighter passenger!



Edit: Just saw Alex's post. Yes, a rattle or mechanical knock in the engine can trick the sensor.

^^^ That's the same as what my mech told me when I had a Cam sensor go... we reset it, it came back, replaced the sensor, no more light.

[robt]

Well if it pops up again I have a spare knock sensor. Its just the hardcore spot it lives in. Well when I put the new IACV on I will have more room.

[Alex]

Well if it pops up again I have a spare knock sensor. Its just the hardcore spot it lives in. Well when I put the new IACV on I will have more room.

Beautiful thing about the knock sensor is that it needs to be anywhere on the motor.

i.e. anywhere on the motor.

i.e. relocate it.


did it to Dylan's motor, and it was happy. just make sure it has a good earth. Aye Dylan?

[RX25SE]

Alex, Doesn't need to be near the top of the cylinder (near combustion chamber) to work effectively?

[Alex]

Well yes, Jason. That would be ideal. The factory position for the knock sensor is in a bitch of a spot, which is just out of reach (literally by a couple of mm) to get off. You could get it off, but there's no hope in hell to get it back in. There's simply not enough room, to get the bolt back on with a deep socket, and maintain the correct thread. I relocated Dylan's one about 20mm from where it originally was, and within easy access. Loom reached with no issues. Important to note, that it requires a good earth from the bolt and the contact surface, so the sensor can complete its circuit.

[RX25SE]

Fairy nuff.

[robt]

Well plugged in the black connectors when I got to work to see if I got any codes. All clear.

[RX25SE]

On a Suby does this give current or history codes??

[robt]

Yes once you pull a code does it delete afterwards?

[RX25SE]

No, you're only reading it. There will be a 'clear codes' procedure but I don't know how to do it on a Suby without looking it up. Anyone??

[Soop]

Gen 2, there a two plugs under the dash. Two black ones and two Green ones. Join them together and turn the ignition on. Shit will happen on the dash, so you'll know its worked. Turn the ignition off. Turn the ignition on again, and start the car. Drive the car untill the CEL light flashes. Stop turn it off, unplug the plugs and you're done.

[twinturbosubaru]

LOL, yes PITA to get to, but it can be done by super mechanic :-0 I changed mine as Alex mentioned, but a swift blow with the hammer to the pesky heat shields fixed the problem :-) Regards Paul

[robt]

Well my old KS has a big crack running through it and it is impossible to get at so I got my spare and put it here: