Check Engine Code=Knock Sensor, Could it be a false indication

I'm not a DIY'er, but I want to not throw money away at possible wrong
repairs.

1997 Legacy 2.2l

6 months ago my check engine light came on and the code read at Auto
Zone was "Knock Sensor" It was suggested that the part could be
faulty, could be a wiring short (intermittent). The check engine
light comes and goes. It almost always comes on after 1/2 hour or so
at highway speeds. I've never notice it go out while driving once it
comes on, but sometimes it's just off when I turn the car on again.
I've never heard knocking under heavy acceleration when the light is
on.

My question is whether that particular check engine code is prone to
indicating failure in a component which is incorrect, ie something
else is wrong (and whatr that might be). This sounds like around a
$200 mechanic repair (diag, part, labor). It's not a lot, but I'd
like not to have the same code pop up again after installing a new
part.

TIA

Check the connection to the knock sensor. I've had a loose connection there
throw a knock sensor code before. Removing the connector and reattaching it
solved the problem. Since you don't mention either way, if your Legacy has
a turbo, ensure you are burning the proper fuel as per the manual.

~Brian

<kaplan3jiim (AT) comcast (DOT) net> wrote

I'm not a DIY'er, but I want to not throw money away at possible wrong
repairs.

1997 Legacy 2.2l

6 months ago my check engine light came on and the code read at Auto
Zone was "Knock Sensor" It was suggested that the part could be
faulty, could be a wiring short (intermittent). The check engine
light comes and goes. It almost always comes on after 1/2 hour or so
at highway speeds. I've never notice it go out while driving once it
comes on, but sometimes it's just off when I turn the car on again.
I've never heard knocking under heavy acceleration when the light is
on.

My question is whether that particular check engine code is prone to
indicating failure in a component which is incorrect, ie something
else is wrong (and whatr that might be). This sounds like around a
$200 mechanic repair (diag, part, labor). It's not a lot, but I'd
like not to have the same code pop up again after installing a new
part.

TIA

kaplan3jiim (AT) comcast (DOT) net wrote:

I'm not a DIY'er, but I want to not throw money away at possible wrong
repairs.

1997 Legacy 2.2l

6 months ago my check engine light came on and the code read at Auto
Zone was "Knock Sensor" It was suggested that the part could be
faulty, could be a wiring short (intermittent). The check engine
light comes and goes. It almost always comes on after 1/2 hour or so
at highway speeds. I've never notice it go out while driving once it
comes on, but sometimes it's just off when I turn the car on again.
I've never heard knocking under heavy acceleration when the light is
on.

My question is whether that particular check engine code is prone to
indicating failure in a component which is incorrect, ie something
else is wrong (and whatr that might be). This sounds like around a
$200 mechanic repair (diag, part, labor). It's not a lot, but I'd
like not to have the same code pop up again after installing a new
part.

TIA
In addition to the post about wiring, a vehicle that age could also

have some carbon deposits built up in the engine that might make it a
little more likely to exhibit knock - particularly after 1/2 hour at
highway speeds. And you could try experimenting with higher octane gas.
If the problem persists at the same rate as with lower octane - I'd
suspect an intermittent knock sensor. If the problem goes away -
possibly carbon deposits or ???

Carl


--
to reply, change ( .not) to ( .net)

On Tue, 20 Mar 2007 21:29:57 -0500, kaplan3jiim wrote:

I'm not a DIY'er, but I want to not throw money away at possible wrong
repairs.

1997 Legacy 2.2l

6 months ago my check engine light came on and the code read at Auto
Zone was "Knock Sensor" It was suggested that the part could be
faulty, could be a wiring short (intermittent). The check engine
light comes and goes. It almost always comes on after 1/2 hour or so
at highway speeds. I've never notice it go out while driving once it
comes on, but sometimes it's just off when I turn the car on again.
I've never heard knocking under heavy acceleration when the light is
on.

My question is whether that particular check engine code is prone to
indicating failure in a component which is incorrect, ie something
else is wrong (and whatr that might be). This sounds like around a
$200 mechanic repair (diag, part, labor). It's not a lot, but I'd
like not to have the same code pop up again after installing a new
part.

TIA

Try high octane gas, if the light goes out, then the knock sensor is doing
its job by detecting the knock. If it does not go out, then it could be a
bad sensor or some other problem with the sensor. Or some other engine
component knocking and the sensor is legitimitely letting you know.

I lean to think that the sensor is just doing it's job.

The light should go off after 2 or 3 trips with no fault.

Are the spark plugs of the right temperature range? You can take them
out and see if there is carbon build-up. When the carbon gets hot, it
changes all the dynamic in the cylinder. Check the gap and ignition
timing too (even if the latter cannot be adjusted).

The fact that the sensor alerts you after 1/2 hour indicates it could
be engine temperature related.

I doubt the problem is caused by the fuel/air ratio because the codes
would be different.

Try using different fuel as dnoye suggested

Good luck

kaplan3jiim (AT) comcast (DOT) net wrote:

I'm not a DIY'er, but I want to not throw money away at possible wrong
repairs.

1997 Legacy 2.2l

6 months ago my check engine light came on and the code read at Auto
Zone was "Knock Sensor" It was suggested that the part could be
faulty, could be a wiring short (intermittent). The check engine
light comes and goes. It almost always comes on after 1/2 hour or so
at highway speeds. I've never notice it go out while driving once it
comes on, but sometimes it's just off when I turn the car on again.
I've never heard knocking under heavy acceleration when the light is
on.

My question is whether that particular check engine code is prone to
indicating failure in a component which is incorrect, ie something
else is wrong (and whatr that might be). This sounds like around a
$200 mechanic repair (diag, part, labor). It's not a lot, but I'd
like not to have the same code pop up again after installing a new
part.

TIA