alan_turbo2000

hi all,

recently my car started bringing up the check engine light randomly staying on for a short period of time then going back off

now on most occasions the car would hesitate under load just before it came on then it would light up and eventually go back off

i done the diagnostic thing with the plugs and it came up with code 22 only

any way i got a knock sensor from east sussex subaru spares and it seemed fine no damage to it but it had a wire coming straight from the sensor were as the 1 on mine had a second plug at the sensor end though the plug that fitted to harness was the same and the sensor head was the same

anyway fitted it and the check engine light was on constant not going off at all and also hesitant under load yet again but now constant

i havnt reset the ecu yet could doing this clear the cel or would that happen anyway after changine the sensor ?

thanks for any help info

wrx271

iTrader: (1)

Why would you assume the sensor is at fault and that there isn't another problem ?

alan_turbo2000

because its my understanding that on a classic the ecu dont bring up the code 22 for detecting knock only a faulty sensor

classicgc8

iTrader: (4)

Hi Alan , I.d source a new sensor..I fitted two second hand ones with no obvious cracks only to find the same issue...your understanding on cel for faulty sensor only is correct. New sensor 70 quid.

alan_turbo2000

Great stuff mate thank you will get a new 1 ordered

Gambit

iTrader: (6)

The important thing is not to over torque the securing bolt, its only something like 15nm / 19lbft

alan_turbo2000

It's 23nm isn't it ? That's what I used

Gambit

iTrader: (6)

I can never remember its something like that. Id a load of trouble with mine a few years back, replacement sensor fixed it.

alan_turbo2000

Fingers crossed in the morning when I re-connect the battery it will be sorted

I'm not holding out too much hope like I'm not that lucky lol

chocolate_o_brian

iTrader: (22)

Are you sure it's not the wiring to the sensor itself?

I had exactly the same thing happen on my last Impreza. So I did as you have and changed the sensor for a new unit. Got a genuine one from Import Car Parts for about £66 delivered.

Didn't change anything.

Called Richard Henry Motorsport up and popped through. It ended up being the wire off the loom to the ECU - was damaged somewhere and is a relatively unknown but common fault (especially on later classics). The wire was cut at both ends and taped off. A new wire was connected and insulated separately from the loom and run from the knock sensor through a spare grommet in the firewall into the back of the ECU.

Quick check of the fault codes and ECU reset - problem gone.

HTH