DTC P0325 – How To Replace a VQ35 Knock Sensor

DTC P0325 – How To Replace a VQ35 Knock Sensor

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OBDII trouble code P0325 indicates an issue with your Nissan or Infiniti knock sensor, or knock sensor wiring. The specific language for the P0325 DTC is knock sensor circuit malfunction. This means that the wiring harness in your engine bay has somehow become damaged, or your knock sensor has failed.

The knock sensor in your VQ35 informs your ECU of dangerous preignition, or knock. This sensor is basically a simple piezoelectric element that detects engine knocking or preignition and translates this vibration into voltage. The ECU reads this voltage and takes the appropriate action, either by curbing or decreasing ignition or increasing fuel.

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The Infiniti or Nissan OE part number for this knock sensor is 22060-2A000, although the same knock sensor can be sourced from a turbo Volvo. The Volvo part number is 13676440.

Today we’ll be showing you how to replace a VQ35 knock sensor in a 2005 Infiniti G35 with the 3.5 liter engine in it. This repair can be done, but should not be undertaken by everyone. Understand that while your knock sensor is just a simple sensor, your intake manifold and fuel rail require disassembly. Not only that but your intake runners and engine will be open to the elements, and all it takes is one nut, washer or socket to fall in to ruin your project.

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Things to consider before undertaking our How To Replace a VQ35 knock sensor DIY guide :

  • Disconnecting your DBW throttle body may require reprogramming your accelerator pedal, as well as idle conditions. This may require a trip to the dealer if our How To Program a VQ35 Accelerator Pedal Guide does not help. Check here on how to test the VQ35 pedal.
  • Your fuel injectors and fuel rail will require removal for access to your knock sensor
  • You might want to schedule other modifications or maintenance items at the same time, such as intake manifold gaskets or even spacers. Click here to see our How To on Installing a VQ35 Intake Plenum Spacer.

Before you begin our How To Replace a VQ35 knock sensor DIY article, you will want to disconnect the negative terminal to your battery.

Open your hood and remove your VQ35 engine cover by undoing the 10mm nuts and the two 10mm bolts in back of said cover.

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The intake system and mass air flow (MAF) sensor and housing must be removed in order to access your throttle body. Remove the 10mm bolts that run through the intake snorkel and loosen the worm clamps on all of your intake couplers.

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Be careful when removing the accordion like intake coupler, as rips and tears can occur if you are rough.

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Remove your ram air ducting and intake box along with air filter housing by undoing the long 10mm mounting bolts.

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Disconnect your MAF by unplugging the wiring harness, and then remove your entire intake snorkel. Don’t forget the 10mm bolt that connects your upper intake manifold to the plastic mid pipe of your intake system.

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You should now be able to see your throttle body and the electronic connector that you should try to keep intact. To do this, you must keep your coolant lines connected to the bottom of your throttle body, and undo the four throttle body hex bolts.

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If you are using a metric hex, this will be a 5 if you are using TORX or safety hex sockets, try a T30.

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Here’s a look at the lines that you will have to disconnect to remove the intake plenum itself from the lower portion of your Infiniti or Nissan 3.5 liter VQ35 engine.

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You should now have your throttle body removed, and your gasket safely tucked away for reinstallation when you are done with our DIY guide. Next, begin undoing all the 10mm bolts that hold all the wiring brackets to your intake manifold. Do not bother disconnecting the wiring harnesses from these brackets, simply disconnect and push aside.

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Start making your way around the outer ring of your upper intake manifold plenum. Remove all 10mm bolts and nuts from the outside of the VQ35 intake, and then you can move on to the longer inner bolts.

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Keep the longer inner bolts separate, as you will be re-installing your intake manifold and tightening the bolts in sequence.

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With all the mounting bolts removed from the upper portion of your intake plenum, you can pull up to remove. You may need to use a dead blow hammer to break loose the upper half of your VQ35 intake manifold.

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After removing your top half of the intake plenum, lift up and clean the intake manifold under your stock gasket.

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Take care as to not pinch or bend this gasket, as you don’t want this to leak and it can be delicate.

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After you are done cleaning, it’s time to address the inner bolts that connect the lower half of your upper intake manifold to the intake runners.

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Remove all these bolts to slide the lower half off your engine.

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With these bolts removed you should now be able to access your fuel rail and fuel injector clips.

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Take some time now to clip the plastic retaining rings around your fuel injector harness. Do not pull these from your plastic valve covers, simply use a needle nose plier to squeeze the end and push through the slot.

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You can take one of two paths here in our How To Replace a VQ35 knock sensor DIY article, one is to undo your fuel injector clips and push the harness out, or two leave the injectors connected.

Because your knock sensor is connected underneath the manifold and fuel rail, you will not be able to completely free your fuel rail and injectors from the engine. This can create a very dangerous situation, as small objects can fall into your engine. Injectors have orings, the fuel rail has plastic spacers and bolts.

We’ll be undoing the fuel injectors in our guide, because that’s just one less bit of risk we’re willing to take.

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Undo the 12mm bolts that run through the fuel rail, there are four total. When you have these bolts removed, you must disconnect the back half of your harness before removing your fuel rail and fuel injectors.

There are two securing 10mm bolts that hold the wiring harness in place. One on the passenger side water pipe that holds the lower chassis harness, and the other on the back of the intake manifold.

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Undo both of these 10mm bolts and now you are ready to remove your fuel rail and fuel injectors.

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You’ve got the fuel rail off and now you can access the bolts that hold the lower intake runners to the cylinder heads. Remove these 12mm bolts and then gently lift up to remove the lower runner assembly.

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Make sure your wiring harness is pushed back and out of the way to prevent any cracking wiring loom or debris from falling into your VQ35 engine. Don’t forget to collect all of your plastic fuel rail spacers either, these are important to maintaining proper fuel delivery and intake manifold seal.

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Remember to take extreme caution as to not drop or have anything fall into your motor, or else you’ll be removing a lot more than your intake manifold.

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With the lower runners removed, you should now be able to see the top of your VQ35 engine and the culprit that’s causing your P0325 trouble code. Remove the 12mm bolt to complete our How To Replace a VQ35 knock sensor DIY article, and replace it with your new unit.

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Unplug the blue knock sensor connector, and then install your new knock sensor and tighten to specification. Reconnect the knock sensor harness and you now know how to replace a VQ35 knock sensor.

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That does it for our DIY guide on a VQ35 knock sensor and How To Replace one to fix a OBDII P0325 trouble code. If you have any questions about this guide, or the knock sensor on a 3.5 liter Infiniti, please leave them for us below!

2 COMMENTS

    • Hi James, thanks for reading.

      This is not an easy job, nor should it be taken as such. It’s not overly difficult but the margin for error is slim, as you can expect because the intake manifold is off and the runners are open to the elements.

      If you feel as though you are handy enough to handle it, I’d say go for it. Not that hard, again just need to make sure nothing falls into the engine.

      Thanks for commenting, let us know how it turns out!

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