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Chevrolet Silverado 1999-2006: How to Replace Knock Sensors

A bad knock sensor can cause some serious engine damage. Before that happens, check out this handy guide on replacing knock sensors in your Silverado.

By Brett Foote - June 17, 2015

This article applies to the Chevrolet Silverado GMT800 (1999-2006).

Knock sensors play an important as well as essential role in your Silverado's engine functionality, detecting any engine noises caused by early detonation and adjusting the ignition-timing accordingly. When a knock sensor fails, detonation is not properly regulated and serious engine damage can occur, leading to some very costly repairs. Symptoms of a bad knock sensor include a check engine light, loud thumping noises coming from the engine, or shaking, vibrating, and misfires on a cold start. Keep reading as this article will show you how to replace a faulty knock sensor in your Silverado before costly damages occur.

Materials Needed

  • 1/4" and 3/8" drive ratchets
  • 22mm deep well socket
  • Torque wrench
  • Fuel line removal tool
  • Replacement knock sensors (2)
  • Knock sensor sub-harness
  • Intake manifold gaskets (optional)
  • Shop rags or small container
  • RTV sealant

Pro Tip

In addition to replacing the knock sensor, preventative maintenance can further reduce detonation.

  • Lower the compression ratio
  • Use higher octane fuel
  • Add injector cleaner into the fuel tank
  • Retard the ignition timing

Step 1 – Access the intake manifold

  • Always disconnect the negative battery terminal (black cover) when working under the hood.
  • Remove the intake hose by loosening the hose clamp on each end: one by the MAF and the other by the throttle body.
  • Then, remove the throttle cable and cruise control cable from the throttle body. If you have a 2003 and up Silverado, you also need to unplug the drive-by-wire harness.
  • Remove the throttle cable bracket from the intake manifold, and push the bracket along with the cables off to the side.
  • Unbolt the main engine harness bracket on the driver's side of the intake manifold.
  • Unplug the EVAP solenoid, MAP sensor, and knock sensor sub-harness.
  • Remove the throttle body and set it aside.
  • Remove the vent hoses from each valve cover.
  • Relieve fuel pressure through the Schrader valve on the fuel rail crossover, and use a rag or small container to catch any gas run off.
Figure 1. Push the center pin of the Schrader valve to relieve pressure.

Step 2 – Remove the fuel lines

  • Use a fuel line removal tool to disconnect the fuel lines from the fuel rails. The fuel rails are located at the rear, driver's side of the intake manifold. Use a rag or small container to catch any loose gas.
  • 1999 to 2003 Silverados have a supply and return line, while 2004 and up Silverados do not have a return line.
  • Use the fuel line removal tool to remove the EVAP line located between the engine and the firewall.
Figure 2. Remove the fuel lines from the fuel rails.

Step 3 – Remove the injectors and engine wire harness

  • Unplug as well as remove all eight fuel injectors and connectors.
  • Disconnect the vacuum line from the brake booster.
  • Pull the engine harness to the side, and unplug the alternator connector.
  • Unplug the idle air control valve.
  • Unplug the throttle position sensor on the throttle body.
Figure 3. Unplug the fuel injector connectors.

Step 4 – Replace the knock sensors

  • Remove all of the intake manifold bolts in the reverse order to their bolted down sequence (10 to 1). Refer to Figure 4 below.
  • Pull the manifold off. The knock sensors are located underneath the black plugs connected to a wire harness.
  • Pull the plugs out and unbolt both knock sensors using a 22mm deep well socket.
  • Install the new sensors and torque them to exactly 15 ft-lbs.
  • Apply some RTV to the rubber plugs to prevent water from entering.
  • Figure 4. Diagram with intake manifold bolt sequence.
  • Figure 5. Unplug the wire harness, remove the knock sensors, and apply RTV sealant.
  • Figure 6. Installed knock sensors with RTV sealant.

Step 5 – Re-install the removed components

  • Clip the new intake manifold gaskets to the intake manifold. Make sure all of the surfaces are clean.
  • Set the manifold back onto the engine, and torque the bolts in their correct order (1 to 10). Refer to Figure 7. First torque each bolt to 44 in-lbs, and then to 89 in-lbs.
  • Put the throttle body back in place, and torque it to 106 in-lbs.
  • Connect the knock sensor plugs from the wire harness.
  • Plug in all the remaining sensors.
  • Reconnect the fuel lines, EVAP line, brackets, and intake hose.
  • Reconnect the negative battery terminal (black), and start the truck to ensure the engine knock has disappeared.
Figure 7. Intake manifold bolt sequence with torque specs.

Featured Video: How to Replace Engine Knock Sensor in Silverado

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