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Knock sensor circuit

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nek

10+ Year Contributor
832
9
Apr 17, 2009
Pittsburgh, Pennsylvania
I dont know much about how the knock sensor works and the more I read the more confusing it gets (I do know what its for.)
Anyways, I am getting a knock sensor circuit malfuntion (dtc 0325) so I disconnected my sensor today and took some pictures.

Is this what is causing my issue?
Is this oem or replacement (I thought I replaced it a year ago but it has mitsu numbers on it).

See Pictures. Its a two wire system, what does each wire do?
Any info added is appreciated.
 

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That looks nasty if any wiring issues are there that could pose a problem, easy fix, get a new one and clear the code then your good to go, that should be the end of that.
 
Sorry to thread jack but I'm having a really hard time getting my knock sensor out to replace it, what type of wrench did you use and how did you get at it? I was trying from the driver's side reaching under the intake manifold
 
If replacing the sensor with a known good one made no difference then I would suspect the wiring harness, particularly the sensor signal wire that runs back into the ECU. That code is thrown when the sensor output voltage seen by the ECU does not change more than 0.06V for more than 100 crankshaft revolutions, which can occur if the sensor picks up electrical interference, or loses it's voltage by the signal being grounded anywhere other than through the ECU sensor ground reference (pin 92 on a 2G).

Test by unplugging the wiring harness from the ECU and making sure the knock sensor pin (the harness side, not ECU side) does not have continuity with chassis ground.
 
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Delta- I have this same problem with my 1g. I know its my harness wiring causing interference. Can I just use new wire and wire the knock sensor directly to the ecu?
 
So you are saying that pin 78 sends the power to the knock sensor and the signal is brough back through the "ground wire" to pin 92 then it is grounded?

I am not very educated on the sensor but I thought that the signal was brought back to the ecu through one wire and the other wire was grounded. No power input needed because its just a microphone.

How many sensors ground off 92?
 
The knock sensor generates a voltage from vibration/resonance and sends that voltage to the ECU through pin 78 (2G) as the signal. Once the signal is processed by the ECU, it goes out of the ECU to sensor ground connected at pin 92. If you cut the wire from pin 92, you'll throw a shitload of DTCs for just about every sensor, since the ECU no longer has a reference to determine what voltages the sensors are returning. The wire connecting to pin 78 (2G) is the wire that I originally said needs to be inspected. The other connector pin at the sensor should be grounded.
 
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1)How does the impressed voltage get to the knock sensor if the knock sensor is just two wires (knock signal output to ecu and ground)?
2)Basically to test the circuit, I would need to test continuity between the sensor signal output back to pin 73 as well as test continuity between the sensor ground and pin 92. I would also need to check to make sure there is no continuity between harness 92 and the chassis.
3)How would I test pin 81?
I appreciate the help.

Edit.....
I think I understand.
The wires on the knock sensor are Input impressed voltage (from 81) and signal output (to pin 78).
Pin 92 is output to ground and the ecu grounds the sensor internally through pin 78. So multiple pins/sensors ground out through pin 92.
By testing harness side 78 vs chassis, you can tell if its grounded any other way but through the ecu.
By testing harness side 78 vs knock sensor harness pin 1, you can tell if there is a short in the wire.
By testing harness side pin 81 vs knock sensor harness pin 2, you can tell if the sensor is getting its impressed voltage.
 
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Well just an update.

I took a multimeter down to my car today and I found that the white wire from the knock sensor side of the harness has no issues connecting with pin 78.

I could not get the black wire from the knock sensor side to match with pin 81 or 92.
Instead, the black wire had continuity with pin 71 and 82... :/ hmmm.

What does this mean?!?

Is it possible that I am only throwing a code at startup and my memory on ecmlink is saving the code? I dont get any cel lights but thats probably just because of ecm link.
 
I'm revisiting this thread to correct some misleading posts I made. I apologize for the errors and not double checking what I posted before now.

This issue has been in the back of my mind recently and I wanted to make sure I had it correct, so I dug out my electrical FSM and here's what I found:

The knock sensor is grounded both to the block and on pin 2 of it's connector and is connected by pin 1 of it's connector to pin 78 of the ECU. It is shown in the schematic as having shielded wire for it's ECU connection.

So my understanding as of now is that it generates voltage on it's own as a piezoelectric device, which is directly fed as signal to ECU pin 78.

nek, ECU pins 71 and 82 are both ignition related.
 
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