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View Full Version : Whats the symptoms of a bad knock sensor?


allante666
11-06-2010, 01:46 PM
My cel sometime comes on at random and slows the car down. Its the knock sensor thats doing it. It pulls the timing to stop it knocking but its not knocking! Sometimes does it as soon as it starts up.
Anyway, i disconnected it and that just makes it stay on, so i disconected it and earthed the wire. That made it go out. Strange thing was though i still got a randon cel, particularly when idling. it was still showing up as the knock sensor!

Do you reckon it simply needs a new sensor?
TGX4776
11-06-2010, 01:56 PM
get the codes read. I just replaced mine and haven't had the cel come back on.
allante666
11-06-2010, 01:57 PM
get the codes read. I just replaced mine and haven't had the cel come back on.

I did. Thats how i know its the knock sensor!
Were your symptoms the same?
TGX4776
11-06-2010, 02:06 PM
the cel was on for my 02 sensors so i got bored during break and ran my codes and It came up. the car ran a bit better afterwards though.
Matty2Hotty
11-06-2010, 03:37 PM
Look for cracks on the black top part of the knock sensor, usually main reason they fail.
phi11
11-06-2010, 03:42 PM
The cel is a symptom,
it's a part that goes bad over time.
I had the cel for the knock sensor in both cars
in the same week.
Repalced both, no more cel.
The sensor in the GT was cracked.(another symptom)
ouch1011
11-09-2010, 12:20 AM
Symptoms will be the CEL on and the car will feel like a dog below about 3000rpm.
allante666
11-09-2010, 03:42 AM
yeah I did actually take it off to compare it with another one i had which was the wrong one as it happens. since ive replaced it the light hasnt come back (so far) maybe a dirty connection. I do have some spare Bosch ones but they all have three wires whilst mine only has one, anyone know the difference? can they be made to work?
ouch1011
11-14-2010, 11:47 PM
Short answer is no. The 3 wire one is probably from a newer model and probably requires input voltage and a ground, whereas the 1 wire one is like an O2 sensor and generates its own voltage.
allante666
11-15-2010, 05:15 AM
Ok Thanks for that. Lights still out btw. The spare ones I had werent even from a Subaru they were off an Alfa but just wondered.