Help identifying wire near knock sensor & P0325 Knock sensor code

[Ryley92]

Hello,
Working on a 99 civic dx 1.6

It's throwing knock sensor no signal codes P0325 & P0330

I first replaced the sensor. No change

Then I ran a cheater wire from the 1 pin on the sensor directly to the corresponding KS pin on the passenger footwell engine ECU connector C ( I believe it's a red/blue wire, might be remembering that incorrectly but it's definitely connected to the KS pin)

No change.
Still getting the same codes which set immediately after reset

I have reset ecu and cleared codes etc.

Then I took a closer look at the wiring harness near the knock sensor (under the intake manifold)

I discovered 1 wire which is yellow/red and it's just dangling there right near the knock sensor

Anyone know what this yellow/red wire I'd or if it's related to the knock sensor codes?

 

[Ryley92]

Update.
I had initially assumed the red wire connecting to the Knock sensor got broken somewhere between the sensor and ECU.

So what I did originally was splice my cheater wire into that red wire on the sensor side, and into the red/blue wire on the ECU.
(Basically in parallel with the [assumed to be] broken connection.

This resulted in the same codes.

However, after cutting the original wiring on both yhe sensor and ECU sides, leaving only my new cheater wire, the code has not come back yet, and since it was setting immediately before, I'm assuming my knock sensor issue is resolved. The original wire must have been shorted to ground or something

I'd still like to know what the yellow/red wire coming out of the main harness, near the red wire of the knock sensor is.

It's completely disconnected just dangling there, and looks like there's some sort of copper toned crimp connection on the end of the wire.
It's hard to see up In that area without taking off the whole intake manifold which, after doing so, would likely make things much more clear.

But so for now, my question remains as to what that yellow/red wire is supposed to be connected to

 

[nd4sped]

You can download the service manual for 96-00 CIvic's on my website. Link is below in my signature.

 

[Ryley92]

I wasn't able to find any information regarding this yellow/red wire near the knock sensors blue/red wire.

However, after doing some different wiring methods after having the P0325 keep getting thrown,
(And without removing the intake manifold to get a better look at the harness to confirm)

I believe I have found the explanation.

Like I said, after the code kept popping back up, it finally clicked how this KS wiring must be.

So the knock sensor itself has 1 single pin, which a 1-wire connector plugs into. This wire is blue/red.

I had originally assumed that wire was shorted to ground or severed somewhere further down the harness.

After running a cheater wire directly from the KS to the ECU, and still getting the same P0325 code, I finally realized what that other wire (yellow/red) was.

Like I said I'm sure it would have become obvious if I had just removed the intake manifold, but either way,

That yellow / red wire must be a ground to shield the KS from interference.

The new wire I had run was still throwing the same code,
I replaced it with a standard power wire from a 19v laptop charging adapter.
(I think any wire which has a metal mesh type insulation around it would work, like even an hdmi or possibly even a higher end USB cable)

Anyway,
Long story long, I'll get to the point

I ran a new shielded wire, and wired the outer metal shielding to body ground, and the code no longer gets triggered.

So I'll confirm for sure tomorrow, when I wire the Knock sensor back to the original blue/red wire, and connect the yellow/red wire to body ground.

This should achieve the wiring as it was engineered to operate

 

[nd4sped]

I wasn't able to find any information regarding this yellow/red wire near the knock sensors blue/red wire.

Took under a minute. Hope this helps.

 

[nd4sped]

FWIW the knock sensor is made of a piezoelectric crystal, when vibration from engine knock are picked up by this crystal it vibrates, generating voltage. So the sensor itself is the voltage source/signal wire. There is no input voltage. The shielding is grounded to protect the voltage signal from being altered. Otherwise the signal may not trigger the ECU to enable the Check Engine Light (CEL).

 

[Ryley92]

FWIW the knock sensor is made of a piezoelectric crystal, when vibration from engine knock are picked up by this crystal it vibrates, generating voltage. So the sensor itself is the voltage source/signal wire. There is no input voltage. The shielding is grounded to protect the voltage signal from being altered. Otherwise the signal may not trigger the ECU to enable the Check Engine Light (CEL).

I did find that page, but it wasn't clear to me based on those troubleshooting steps that the KS had a grounded shielding

Maybe because I can't read a wiring diagram but I didn't read anything regarding a second wire or connection.

It simply says check for continuity between KS and ground there wasn't.
And check for continuity between ECM and KS connector. There was

I'd reset ecu and start engine, let engine idle, no codes.

Then only after driving uphill it'd throw the code almost immediately.
Thanks for the page , and Like I mentioned I did read it but it didn't help me so I was just following up in the hopes it might help someone else in my position

 

[nd4sped]

I did find that page, but it wasn't clear to me based on those troubleshooting steps that the KS had a grounded shielding

Maybe because I can't read a wiring diagram but I didn't read anything regarding a second wire or connection.

It simply says check for continuity between KS and ground there wasn't.
And check for continuity between ECM and KS connector. There was

I'd reset ecu and start engine, let engine idle, no codes.

Then only after driving uphill it'd throw the code almost immediately.
Thanks for the page , and Like I mentioned I did read it but it didn't help me so I was just following up in the hopes it might help someone else in my position

If the wiring is good and you keep getting the same code then you may want to look into why you are getting a knock signal. This could be due to the car running far too lean. This can be caused by a number of issues, faulty fuel pump, fuel pressure regulator, massive vacuum leak, fuel injectors, MAP sensor or even a bad coolant temperature sensor.

I would start with a vacuum gauge and see how much vacuum is produced at 2000 RPM, then follow the diagram diagnostics that is generally included with the gauge kit.

 

[Ryley92]

Final update on the issue,

I rewired the factory blue/red wire to the KS connector (its a grey 2 pin connector with only 1 single pin which is the red/blue wire)

The disconnected yellow/red wire coming off the same harness near the knock sensor I just soldered a u shaped clamp connector to it and wedged it under a bolt in the general area.
I wired the factory red/blue wire going into the C connector of the ecu, and happy to report,

So far the code hasn't come back so I can confidently say problem resolved.

I'll update down the road if the code ever comes back but the shielding being grounded was definitely the solution.

I had meant to loosen the KS a bit while I was in there (which I read can help make the KS less sensitive) but I forgot to do so and had already lowered the car back down.
So far so good though so that wasn't needed.
Just for the record the KS was torqued to 7 ft-lbs with a drop of loctite