Knock Sensor Mystery

[Racemysaturn4me]

I have a 1997 Saturn Sc2 with a check engine light issue. After checking, it showed a P0327 code which is the knock sensor low input. I took it in to a shop and they replaced the knock sensor. It was still showing the check engine light so they replaced it again. Still same issue so the third one I found the GM knock sensor part and they installed that one. They thought that maybe the issue was my car needing the GM sensor as I have had issues in the past with parts. Still having the issue. Where do we go from here? Where is the wire harness on this car and how do you get to it? The knock sensor just connects to the engine. Any help is appreciated. Thank you.

[TomM96]

I dunno much about that sensor; I think NGK, Denso, and Standard
Motor Products are likely to be good quality (with OEM best).

FIF, Fdryer, or BillR are likely to be more informative.

Two things which Might be worth doing:
1. check/clean some harness grounds
2. disconnect battery (& maybe pull fuse for air bag); then
(taking care to avoid static discharge) Remove/Replace the
multipin connectors to the PCM.

[cgg17]

I would advise checking the wiring harness for the knock sensor. I believe on 1997 models, the PCM is underneath the dashboard, which is easy to remove. Check for continuity between the knock sensor wire going into the PCM plug, and the knock sensor connector at the sensor itself.

I am not too sure of which wire/terminal number it is for the PCM side, you will have to locate a wiring diagram for the 1997 model year for that. I only have a set of 1995 manuals to reference from, and they use a different PCM.

Best of luck

[TomM96]

Soooo re-read a post mentioning issues with other sensors.

Maybe check&renew grounds in engine compartment; if they have
different resistances/(impedances) that might effect what levels the PCM can 'read'.

[SRGW]

See attached knock sensor lower right bottom.

1995 SL1 236,300 2005>2018
1997 SL1 93,800 2014>????
CHECK YOUR OIL!!

[Racemysaturn4me]

The check engine light that is putting out this code P0327 is now intermittent. If the check engine light is on for a while and then off and then on again, could that be more likely a wiring issue?

[TomM96]

> could that be more likely a wiring issue?

Sure ... on most days there is greater likelihood of variance in 20-year old wiring, than a recently-manufactured component.

The fact that you've replaced an indicated component a few times ... and
the issue has changed to 'intermittent' from 'constant' condition, is
probably a sign of progress.

Spraying electric contact cleaner onto the harness connector for the
knock sensor might be worthwhile (the re-connection process at that point
may have dislodged some OXIDATION of the metallic surface of the
connector, decreasing the loss at that position.

Metals tend to have low resistance when clean. When dirty, or covered
with oxidation, the resistance to electric flow is often Much higher.

There's a chance some antifreeze or salt spray got into the connector at one time. Even atmospheric contact can eventually tarnish contact surfaces;
at elevated temperatures, the Rate of oxidation is much higher than
at room temperature.

[fdryer]

Racemysaturn4me, several past threads about knock sensor issues were traced back to an unusual issue - worn out belt tensioner hitting its own end stop. The mechanical rattling is heard by the knock sensor and triggers the error code. Examine the belt for looseness as it should be tight with very little deflection when pressing on it with fingers.

[Racemysaturn4me]

"Spraying electric contact cleaner onto the harness connector for the
knock sensor might be worthwhile (the re-connection process at that point
may have dislodged some OXIDATION of the metallic surface of the
connector, decreasing the loss at that position."

I think it's very likely you are right on with this one. I did have an issue with a major antifreeze leak so it probably leaked onto there. As I recall it probably was around that time that I started having codes for the knock sensor popping up. Thank for the advice! I will try cleaning that connector.

[TomM96]

One day under my '97DOHC, i noticed that the corner/edge of the
block above the starter motor flange was coated with some sort of
corrosion (which i guessed may have been a coolant leak). It was of
interest because the starter(s) on that car Never got quite enough
power to crank properly {later guessed excess loss in the transmission
PRNDL/neutral-safety switch}....