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!@#$ Knock sensor

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nek

10+ Year Contributor
832
9
Apr 17, 2009
Pittsburgh, Pennsylvania
My damn car is still throwing this knock sensor circuit code and I cant find any information on the damn thing. Its like no one truly knows how the knock sensor works.
From the information Ive gathered, the knock sensor has 2 wires. One is grounded the other is a signal wire back to pin 78. Easy enough.

Is the ecu supposed to provide the sensor with any voltage?
How much voltage is the sensor supposed to be sending to the ecu with no knock?
How does the ecu know the difference between a knock sensor malfunction and a knock sensor circuit malfunction?


I am getting a circuit malfunction dtc. The ground tests fine and the knock sensor itself is new. I am getting a voltage of 63mv on the signal wire which I think is coming from ecu side of the harness which may be my issue but I cant find any information on the damn specs.:banghead:

Gimme some help, even if its just a link to a informative website.
 
So you tested continuity to ground from the ground on the knock sensor plug?. Did you test for continuity from the signal wire in the sensor plug to the pin on the ecu. Did you also test the signal wire for continuity to ground to make sure that it isn't being grounded out?
 
Bryan, I tested continuity between sensor ground wire and ground and it checks out. I tested continuity between knock sensor signal out and pin 78 and it checks out. There is no continuity between sIgnal and ground. As far as I'm concerned the wires are correct.

Iugrad. That's what I think is the issue. I contacted ecmlink to send my ecu to them but my tsi is my only car so I won't be able to go to work of I send it out so I want to make sure it's the issue. What symptoms was your car having? Ecmlink told me if the ecu was bad it's unlikely the knock circuit malfunction would be the only issue but not to rule it out.
 
IF the wiring check's out and you have a new sensor than the ecu is the only other possibility.
 
There should be 5V coming from the ECU on the 2GS. Looks like it ## ecu. I wonder if you can sub in a 5V signal.
 
Chris. Where do you get this information? I was told by another member that the ecu should feed the sensor 5v but I as I look into it, I think that's false. The sensor creates voltage based on vibration I dont think there is a voltage input. Could someOne clarify? Where does the 5v come from? And what is its purpose?
 
Doing some reading that was bad info. the knock sensor produces a 0-5V signal. What I cant find is how the ECU tests the knock sensor. idk if it uses a voltage or if it tests the resistance of the sensor.
 
The ecu looks for a certain range to filter out other engine noise this is a good website.
And this explains how the ecu reads the voltage which is created by the knock frequency. On the second link scroll down to the picture by The "background information". This could be how our ecu may work except instead of pin3 for shield ground, the shield gets its ground from the sensor mount ground. If this is the case then I dont know how the reference ground gets back to the ecu
 
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