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What other code(s) did you have? The knock sensor code won't trigger the SES light. I've been running the knock sensor bypass mod for 9 years and 110k miles. I could have replaced the sensor fairly easily when I did my valve cover gaskets but I'm happy with the mod, so I didn't bother.

I've been running 87 Octane for the last couple years in my '02 with the S/C. I haven't noticed a difference, honestly. I do have headers installed with the primary cats deleted, not sure if that matters.
 

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Hi there. When I ran the INNOVA a few nights ago these codes came up. P0328 Knock sensor / Circuit B, C1113 G sensor for ABS, P1491 Vacuum cut valve bypass valve.

I too ran 87 octane since Feb and didn't notice any problems. I have started to drive the X more in the last month and the SES light came on about 2 weeks ago. ABS light comes and goes. I have resent everything and put the new tank of 91 oct and the Lucas boost.
 

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Hi there. When I ran the INNOVA a few nights ago these codes came up. P0328 Knock sensor / Circuit B, C1113 G sensor for ABS, P1491 Vacuum cut valve bypass valve.

I too ran 87 octane since Feb and didn't notice any problems. I have started to drive the X more in the last month and the SES light came on about 2 weeks ago. ABS light comes and goes. I have resent everything and put the new tank of 91 oct and the Lucas boost.
The knock sensor is likely failed, but that didn't trigger the check engine light. That can be bypassed, replaced, or relocated so it is easier to replace in the future. You won't notice any difference after the repair, though. Running premium gas could help if you actually had a knocking or pinging issue due to an engine problem...but if the sensor itself is just bad, the gas quality won't change much. My knock sensor looked to have a heat related failure...the plastic sensor was cracked and almost looked melted. My engine ran fine though...but I still ended up replacing it and relocating it to the top of the manifold plenum.

The P1491 vacuum cut valve bypass valve code is what is trigger the service engine soon light. That would be part of the evaporative emissions system. Possibly dry rotted hoses, bad connections, or the valve itself is damaged.

https://www.autocodes.com/p1491_nissan.html

ABS codes...ehh...my truck hasn't had the ABS working since I owned it for the last 7 years...Don't know :)
 

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Thanks a lot Rob. As for the knock sensor, I am going to run two tanks of premium with the Lucas high octane boost and see what happens. The truck sounds and runs great so I am not panicking about it.

I downloaded the service bulletin for the P1491 which triggered the SES light. Going to check the system again in a few days with my INNOVA 3100j and see what comes up. May have to take it to my shop and have the valve evaluated.

Thanks again for the help. Oh, and the ABS is not a big deal to me either. Brakes work fine.
 

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Thanks a lot Rob. As for the knock sensor, I am going to run two tanks of premium with the Lucas high octane boost and see what happens. The truck sounds and runs great so I am not panicking about it.

I downloaded the service bulletin for the P1491 which triggered the SES light. Going to check the system again in a few days with my INNOVA 3100j and see what comes up. May have to take it to my shop and have the valve evaluated.

Thanks again for the help. Oh, and the ABS is not a big deal to me either. Brakes work fine.
The ABS is just the feature to prevent skidding if you apply brakes too quickly or on sick surfaces. May be an issue in snow...

Your brakes will function fine, but the computer won't automatically release your brakes if you start to skid is all.

The evaporative emissions valve and lines are just used for fuel evaporation from the fuel tank. Won't change how the truck drives, but you may get less gas mileage as you get more gasoline losses from the fuel tank and system. You shouldn't need a new fuel tank...I bet you could youtube and find some videos about the valve or vent lines. It could be as simple as dry rotted rubber.
 

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Thanks a lot for the info. The service tech told me the same thing about snow with the ABS. I will get that fixed as I travel specifically in the snow for work in the winter (worked awesome last year - was the only guy on the road - cops were even going home when roads were closed). With snow tires it was great in 4x4. Used low a few times as a bail out - zero issues.

I will leave the valve blow off thing for now. I agree with you. Common sense tells me it is not a big deal. I am pulling 19mpg on hwy so not worried. If it dips to 16-17 on hwy I will get the valve looked at. Might be a hose like you suggest. Fuel tank is fine. Bone dry underneath and no drips on the driveway. Taking it for the three day trip this weekend. Taking tool box ... just in case.

Thanks again for the support. Dave
 

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I'm gonna make this a sticky cause its just talked about so much and recently there has been new information on this topic. If you are getting a PO328/P0325 code on your truck it is the knock sensor and it probably has gone bad but there are other possible reasons for getting the code. You might have gotten a bad tank of gas or your ignition system isn't working as good as it should. I would recommend you fill your tank with hi octane gas or gas treatment, run through that tank and check for the KS code again after you have cleared it and do other repairs before attempting the knock sensor replacement or by pass. Make sure your ignition system is working as it should. If after you have do all that and you are still getting the KS code your KS or harness might be bad. Its your choice to to do the replacement or by pass. We are trying to give you all the information we can to help you in your decision. There is not one good answer for your decision. Some decide to do the replacement. Some decide to do the by pass and some decide to leave it alone. Again the choice is yours!

It seems as though when your knock sensor goes bad the ECM will retard the timing to a preset position in order to prevent your motor from "knocking or pinging". This retard in timing will possibly reduce power and you will get slightly less MPG's but probably not enough to notice in the NA 3.3. In the supercharged 3.3 the ECM will put the truck in "limp" mode and you will notice a major reduction in power. This is to prevent your 3.3 from destroying itself. By doing the knock sensor by-pass you have now removed the safety from the system and will have to be diligent in what type of fuel you run and your driving habits. The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is sensed as vibrational pressure. This pressure is converted into a voltage signal and sent to the ECM. Freeze frame data will not be stored in the ECM for the knock sensor. The MIL will not light for knock sensor malfunction. The knock sensor has one trip detection logic.




#1. Bad knock sensor won't set an SES light. The code was already there when the light came on.
#2. Bad knock sensor will possibly decrease fuel economy.
#3. Bad knock sensor will Possibly retard timing causing a slight reduction in performance but probably not enough to notice without monitoring live data.
#4. Knock sensor bypass should be done at your own risk especially with a SC Xterra.

The red arrow points to the location of the knock sensor:
 

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WOW! Glad I found this post. I have a 2000 SE that my son is driving now. Check engine light came on a few times and have the Knock sensor and O2 sensor code. From reading these posts, it seems that the Knock sensor is not a big issue. Think I'll just leave it alone. How hard is it to replace the O2 sensor. I believe the code I received was for Bank 2, with no activity.
 

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It isn't very hard, but you would need an oxygen sensor wrench...


It can be a bit tricky just due to the heat shield on the exhaust manifold getting wrench access (if it is the primary o2 sensor)

The exhaust has a threaded hole,...and then there is another threaded adapter in the exhaust that the oxygen sensor itself threads into. I only say that because it is common that the adapter comes out of the exhaust with the sensor...and if you don't notice, you may be confused when the new sensor doesn't fit the hole left in the exhaust.
 

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curious as to why you say NOT RECOMMENDED FOR S/C ENGINES? the person who has the DIY write-up on this site is doing it to a S/C engine and sounds like it worked just fine. i'm not saying your wrong - you may be spot on, which is why i'm asking. i have a S/C and am considering doing this mod. i paid to have the dealership replace the original and it made a HUGE difference, for sure, but i still think it's robbing the S/C at times even still, so it would be nice to just make that thing go away. and i ALWAYS use premium fuel (at least 93 octane).
WHO IS THE GUY? I WANT TO DO THAT TO MY 04 SE. THANKS - dern caps
 

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WHO IS THE GUY? I WANT TO DO THAT TO MY 04 SE. THANKS - dern caps
Is your SE Supercharged? From what I remember, there's no real benefit to doing the mod for non supercharged engines. If it is supercharged, like mine, just do the resistor mod. I've been using it for over 120k miles and my truck rarely gets mid grade gas, let alone premium.
 

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I have a 2004 Supercharged and had a po328 code.

The bias voltage is at 4.8 volts per my voltmeter. This would lead me to believe the knock sensor is an open circuit making me think the resistor has failed in the sensor
. The resistor is on a parallel circuit to the piezoid circuit which is effectively a capacitor

I have left the knock sensor in place and simply inserted a 560 k ohm in between the 7 and 8 pins on the green wiring harness plug ensuring I did not short the bias voltage wire to the shield with the resistor.

This has removed the po328 code without taking the piezoid out of the circuit so the knock sensor may still be effective in sensing knock.

This is a temp fix until I have time to do work on the engine and replace the knock sensor. I plan to service the injectors and maybe even do the head gaskets when I do the tear down. Only 180 000 km on this vehicle. So lots of life left.
Does anyone know how the shield wire ground is maintained physically in the cable connector?. My only worry is shorting to that shield.
73946
 

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It's been ten years since I did the resistor mod and I can't remember there being any shielding on the wires I soldered the resistor to. I know I used heat shrink tubing and used electrical tape to wrap the plastic sheathing I cut back to expose the wires. My thought was that I could easily return it to stock if I ever wanted. Never did and never will. It's been a solid solution for ten years and 130k miles. Hell, I wouldn't spend 5 dollars to replace the knock sensor even if it was a five minute repair.
 

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The white wire is thicker than all others and the shielding would cause this. It makes sense that a wire carrying a signal is shielded. I'm assuming this is the case with the knock sensor wire .
 

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I'm no electrical genius but I believe the ECU is only reading resistance on the pair of wires for the knock sensor, not any digital data. I pulled those pins from the connector so there couldn't be any additional resistance in the circuit, but I think you've proved it doesn't matter. I'd check for the code again after a few hundred miles though if I were you.
 

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The bias voltage should be 2.6 volts. The knock sensor sends a signal on that line that the ecu has to analze to determine if it is in fact knock. There can be alot of noise from other events that the ecu has to ignore. The brains are in the ecu not the sensor
 

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That's why I said the ECU reads the resistance (Ohms) on the circuit. Are you suggesting it reads voltage value or possibly amps instead? That could very well be but I wouldn't think either of those values would be effected by noise on the line. All I know for sure is that I eliminated the knock sensor from the circuit and the ECU is satisfied with a 540k resistor in its place. I think noise would only be a concern if the knock sensor were in use, as it's a piezoelectric device.
 

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It doesn't read resistance which would be constant on that circuit at 560 ohms, the path across the crystal functions like a capacitor effectively infinite resistance in a DC circuit . The knock sensor emits a voltage spike when it senses noise by squeezing a piezo electric crystal just like your BBQ starter. The ecu examines the voltage wave and determines if it is in fact a knock. Many bias voltage sensors work in a similar manner with different mechanisms changing the voltage for the ecu to interpret.
 

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ECU examines the voltage wave? Seriously? That's one smart ass ECU. I believe your overthinking this. Just disconnect the knock sensor and trust the 540k resistor in its place will keep the ECU happy. I was under the impression that the knock sensor simply changed the resistance value based on noise/ engine knock and that is the value the ECU is "examining".
 
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