pops

Hi all, my 94 WRX Engine check light comes on/off intermittently after normal operating temperature has been reached. I plugged connectors together under dash and error code 22(two long/two short)., came up. Searching thru' archives i've found that its the "knock Sensor" ?? Is this knock as in fuel problems or a vibration sensor. Where is it ? Can it be changed ?, how much? or can i cure it myself. "HELP"
Thanx.

[Edited by pops - 6/6/2002 8:13:26 PM]

Scott.T

iTrader: (2)

Try Grade A Breaker, he'll probably do you one for about £25. If not they are approx £100+ new.

It's Knock as in 'Detonation'. It's basically a microphone that's bolted to the top of the engine.

It's directly under the throttle cable connection and is a black round thing with a 12mm bolt through it, and 1 wire connection.

You will need a ratchet and extension and 12mm socket to remove it.

You could try to measure it's resistance to 'Ground'.
Disconnect the wire and measure between the wire to the sensor and an earth point, is should be about 540K.

If it only does it when warm, best to get the car up to temperature 1st tho'

[Edited by Scott.T - 6/6/2002 5:35:52 PM]

pops

Thanx for your reply Scott,, will test resistance of sensor, and if it is around 540k could i disconnect it for a short while just to eliminate it from the fault finding process?? Can any harm be done running car with it disconnected? I recently had to fill up with normal un-leaded, could this be adding to problem??? Thanx once again, will let you know how i get on.

Scott.T

iTrader: (2)

If you run with it disconnected the ECU will probably go into limp home mode. Thus only allowing limited Boost.

I believe the knock sensor is used all the time to keep the timing at it's optimum setting i.e just B4 knock occurs. But I may be wrong.......

I also don't believe that detection of knock will cause the ECU light to flash the '22' fault code, but a breakdown in the resistance will.

The ECU expects at start-up to see certain voltages/values from all the sensors, and also expects to see different voltages/values when running. If the voltage/values fall outside ceertain parameters then the Check light will illuminate for that sensor.

One thing you could do is :
1. Run the car until the light appears, turn engine off.
2. Re-start engine to check error still being logged, turn engine off.
3. Disconnect the Knock sensor and fit a 540K resistor.
4. Re-start engine to check error has gone, turn engine off.
5. Re-fit the knock sensor fully (to make ground contact).
6. Re-start engine to check error still being logged. This will then confirm the sensor.

Although I expect when hot the Knock Sensor is 'Open-Circuit' or 'High Impedance'.