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Outback Wagon, 2004, H6 3.0
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Discussion Starter · #1 ·
I have P0328 code which has been intermittent for a few months. My OBD tool tells me
"Knock sensor 1 Circuit High Input (Bank 1 or Single Sensor)". Bank 1 means passenger side correct?

I have just installed a new sensor without removing intake manifold. With help of dental floss and a magnet. Was very proud of myself. Start the car the CEL comes right on. What's the deal? Could I have ruined new sensor by overtorquing it? Reset the code, comes right back.
What is that bit about angle (see the pic below). I installed exactly as the old one was sitting - with connector side looking back. Very frustrated.

511574
 

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Outback Wagon, 2004, H6 3.0
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Discussion Starter · #2 ·
OK. I crudely checked the sensor I took out by clamping it to a sledgehammer and then whacking it with another hammer while measuring A/C voltage between sledgehammer and one of the sensor contacts. I see it is responding. Whether or not it is within the specs - I don't know. I guess this means circuit is bad. This is bad news as it means taking off the manifold to check it. Oh boy.
 

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Outback Wagon, 2004, H6 3.0
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Discussion Starter · #3 ·
Trying to summon @cardoc who has written extensively on p0420.
I used to have p0420 and I replaced driver side cat, 02 sensors, down pipe and muffler 2 years ago. Non OEM cat. Passenger side cat and oxygen sensor are original. Could that be a possible cause of p0328. Grasping for straws really.
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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This code means the ECM is not getting the correct resistance feedback from the knock sensor. It's either too much space between the plates, a bad connector or there's a break in the knock sensor wire to the sensor. To get a good look at the knock sensor wires you would have to remove the intake manifold. Have a pair of gaskets handy and before you put the intake back on make sure all the old gasket is removed from the intake and the heads.

And aftermarket knock sensors don't work.


511680


511679
 

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I don't see any possible link between a P0420 and a P0328.

The P0328 is an electrical fault. The one wire from the sensor goes to the ECM. The ECM monitors that connection both for knock signals (sort of a short AC signal) and DC voltagehe voltage. Normally the DC voltage should be between 2 and 4.7 V, but if it's more than 4.7 V for a second, that triggers the P0328 code. (The "high" in the description indicates the voltage is higher than it should be.) As the knock sensor itself doesn't generate DC voltage, it has to be coming from elsewhere. That could be a short between the knock sensor wire and another wire that is at a higher voltage, e.g. one carrying battery voltage, or although unlikely, a fault in the ECM. (See attached "criteria" pages.)

@cardoc It seems to me that the FSM diagnostic tests (above, and in the FSM I have) are incorrect for a "high" fault. The detecting criteria for the "High" code is the existance of > 4.7 V DC, whereas the diagnostic tests look for a low resistance, or short, to ground that would pull the voltage low (< 2 V). The latter is more consistent with the P0327.
 

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Outback Wagon, 2004, H6 3.0
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Discussion Starter · #6 ·
Thank you both. The reason I alluded to p0420, was thinking that that p0320 could have something to do with what it measures , that is knock, and since that is related to ignition, I thougt that 02 feedback signal could do something with it.
But you essentially state that the issue is with DC voltage in that single wire. BTW, the KS I put in is made by Subaru. And the old one seems as good as new , and generates some AC voltage when I crudely tested it. So yes, I agree I need to check the wire. What a PITA having to unbolt the manifold , power steering pump. Change the Gasket, just to get to the wire. Typical Subaru experience.
 

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@mitka

Do your knock sensors have one or two pin connectors?

If one wire, then I believe it important/critical that there's a good electrical contact between the knock sensor and the engine block.

According to the ECM I/O (input/output) table, with the knock sensor connected, there should be 2.5 V on the wire going between the sensor and ECM. (This voltage is monitored by the ECM at the ECM connector, B135 pin 4 in the diagram posted above.

I was puzzled why the voltage is being applied to a piezoelectric element, which generates voltage on its own. But this article provides a reason, namely, circuit integrity. In this case, if the voltage is around 2.5 V, the circuit is intact, but if it's higher (in the example, 5 V), it indicates a problem, such as the knock sensor being unplugged. The Subaru P0328 is probably the same; normally there's 2.5 V, but if it's >4.7 V, it triggers the code. @cardoc was right on this.

That suggests a possible bad connection between the knock sensor and ground, a bad connection along the wire back to the ECM, a bad connection at the ECM, or, as noted earlier, a fault in the ECM or a short between the wire and a source of the higher voltage. Perhaps before removing the intake, verify the contact surfaces between the sensor and the block, and if the sensor harness connector is accessible, check continuity between the connector and the ECM. Alternatively, using a digital multimeter measure the voltage at the connector nearest the knock sensor (E14 in the diagram above) with the ignition at On, engine not running. If it's 5 V then there's a discontinuity between the connector and the knock sensor ground to the block. If it's zero V, then there could be a discontinuity between the connector and the ECM.

Incidentally, what's the resistance between the single connector pin on the sensor and the sensor metal base that contacts the block (or between the two pins of two-pin sensor connector? A used (for spare) two-pin sensor I have for my 07 measures around 4.7 MegOhms. This is higher than most sources suggest, so not sure if it's good, consequently the interest in the resistance of yours. Note: It takes some time for the meter to reach a stable reading because of the high resistance and the piezoelectric element. (Some multimeters might not have a high enough resistance range.)

p.s. ScannerDanner has good videos on this particular code:


 

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2001 2.5 RS & 2000 OB
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Knock sensors can ground through the block. If you don't have a good engine to chassis ground, that's half the circuit right there.
 

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Outback Wagon, 2004, H6 3.0
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Discussion Starter · #9 · (Edited)
@plain OM

Thanks.

Single wire. Yes , I explored these videos. I mean it all boils down to do voltage measurements on connector and going from there. The problem is that I can't do it without removing the intake manifold. I have H6. Can't reach whatsoever without doing it.

Some more info. When I was replacing the sensor, which by itself was not a small feat, I realized that I displaced my OBD Bluetooth dongle. So I reset ECU by disconnecting the battery. When I reconnected the battery and started the car, the CEL lit right on. May be I did not really reset the codes. Since then I purchased another dongle and reset code via an app. So far it has not come back. Keep fingers crossed as I am not looking forward to taking off the manifold, PS pump, replacing gasket etc.
 

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There might be another way to help narrow it down.

I appreciate that the connector right at the sensor can't be accessed.

There's two other possible access points in the wiring between the sensor and the ECM; in the attached wiring diagram (also wiring diagram above by @cardoc), there's the E2/B21 connector pair, and the B135 connector at the ECM.

I'm not very familiar with the H6 layout, but according to the FSM, the E2/B21 pair is one of three pairs at the back of the engine, near the bell housing.
511904


Is it accessible?

If so, and if the code reappears, then if the two connectors are separated, that might be a point to make measurements that could determine whether to focus further attention under the intake, or in the wiring between B21 and the ECM.

Incidentally, I've confirmed that the used sensors I have from a pick-n-pull yard are both missing an internal resistor and that's why they both read very high. The factory-installed sensor on my engine, which I was able to measure today, reads about 560 kOhms, which is consistent with the FSM. Also, cardoc confirmed the same for the knock sensors in a 2002 H6.
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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The H6 I tested the knock sensor on was a trashed engine on a crate here in the shop. It does not have the harness on it since I had to transfer the harness to the replacement engine. The knock sensor is a 2 pin sensor but the harness connector is a single wire. I erred in my assumption of a 2 wire connector based on a 2 pin sensor.

To test the sensor all that you need to do is check between the two pins.

@yarrgh

The ground is dependent on it's connection to the battery, not the body to engine. The engine is grounded via the negative post on the battery through the main ground cable. The body is grounded via satellite grounds from the main ground cable and connections between the engine and body. The transmission gets it's ground by it's connection to the engine block. The knock sensors are grounded by their connection to the block. The alternator and AC are grounded through the block. Pretty much everything on the car is dependent on the main ground to the block because without it nothing works proper, if at all.

Body grounds are important for the lights, wipers, accessories inside the car, keyless entry, ABS or VDC systems, and all the switches inside the car.

And keep in mind that electrical flow is from the negative side to the positive side. And before anyone starts talking about fuses on the positive side, when a fuse blows it's like turning a switch off and current back to the battery stops. Accessories with a direct connection to the positive side are controlled via a switch which controls the ground feed and will work until a fuse blows. Accessories with constant connection to ground are controlled by positive feed and allows current to flow through that accessory unless a fuse blows and stops it. Without electricity flowing, that part doesn't work. So in the case of the knock sensor, something is stopping flow from the ground to the computer.
 
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