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How To

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Knock Sensor Replacement

This 2004 Chevy Silverado pick-up truck has a persistent engine light on and it's time to get this taken care of.

If you’re visiting this project from the DirtyShirt YouTube channel you’ve probably already read the comments from some of the other guys who state that we made the project harder than it really is.

That may be but keep in mind that we’re not professional mechanics and we’re not trying to get this job done and out the door according to a time clock.

If the manifold can be released from the block and rolled out of the way to get to the sensors then that is what we’d recommend you do – we didn’t do it that way. That approach comes with its own set of problems and inspection and cleaning would seem to be a lot more difficult with the intake still connected with wiring harnesses and the rigid fuel supply line.

*Note again that this is a 2004 truck being discussed in this project. The torque specs and procedures we used are from the 2001 CK-8 five-volume service manual set. Use this information at your own risk.

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Jeff describes the code we pulled from the ECM and then we get into some of the things we did to remove the manifold and access the knock sensors.

knock sensor before disassembly

Here’s a shot of the engine before disassembly. As is our custom we’ll snap quite a few close-up still pictures in case we need to refer back to them during reassembly.

knock sensor intake removed

The video describes how we got to this stage but as this shot demonstrates we’ve removed the intake which enabled us to inspect the part. The fuel rail is still loaded with fuel so be prepared for the gas to run out of the manifold as you do your inspection and cleaning.

knock sensor in context to block

For whatever reason the manifold does not come into contact with the valley between the heads – this is clearly by design. The problem is that water (rain spray – not coolant) can collect and run through the valley. That is what happened with this truck – water probably entered at the front of the valley, ran to where the rearward sensor is located, the protective boot over the sensor leaked and water remained in the sensor hole and essential submerged it in water. We believe this is what caused the sensor to fail.

knock sensor old front sensor

Here’s a top-down shot of the front sensor.

knock sensor old rear sensor

Here’s a top-down shot of the rear sensor. It is covered with corrosion and it is a different color than the front sensor or a new sensor.

knock sensor old

These are the connector plugs from the old harness that ran to the old sensors. The connector at left was connected to the front sensor and the one at right to the rear sensor. The piece in the middle belongs to the top of the rear sensor – is broke off when we removed the wiring harness.

knock sensor stuck removal

The sensors are configured so that a socket can be used for deinstallation and installation. The old rear sensor had so much corrosion that it would no longer accept a properly sized socket and allow us to break it loose.

Our solution was to obtain a socket with a similar diameter as the largest part of the sensor. We attached a 6” socket extension to the socket and hammered the socket onto the sensor until it bit into the sensor’s metallic body. We attached a ratchet to the extension, gave it some muscle and the sensor broke loose.

knock sensor removed

The old rear sensor after removal.

knock sensor new

An example of a new sensor.

knock sensor new wiring harness

An example of a new wiring harness.

knock sensor post installation

The intake ports of the heads were blocked with rags and we went to work cleaning all of the surfaces. Both new sensors have been installed and torqued to Metric 20 N.m or English 15lb ft.

knock sensor new harness installed

The new harness has been installed and silicon has been applied around the rubber plugs that protect the sensors from dirt and water.

knock sensor intake manifold rigid gaskets

The new intake gaskets are rigid and snap onto the intake manifold. The manifold mating surfaces were cleaned and the gaskets were installed.

knock sensor bolt torque order

The intake manifold is held to the heads with 10 bolts. The tightening sequence is shown above and the torque specification for these bolts is as follows:

  • First pass in sequence – Metric 5 N.m, English 44 lb in (inch not foot pounds)
  • Second pass in sequence – Metric 10 N.m, English 89 lb in (again, this is inch-pounds)
knock sensor bolt torque

Evan is putting the final touches on this job with a torque wrench. We started the truck, checked for leaks and noted that the engine light remained off.