How to Bypass a Knock Sensor

A knock sensor is part of your car's ignition system. The computer in your car electronically advances the ignition timing, till the time the knock sensor is able to detect the ping. Once it reaches that point, the car computer backs off the timing until the pinging stops. The sensor ensures that the engine produces power without pinging. Pinging is just what it sounds like; a knock or ping sound coming from the engine when your car accelerates. Pinging can be caused by lower octane fuel, an overheating engine or having your spark advance set too high. If you are receiving a trouble code from your car's computer, it is possible to bypass a knock sensor for troubleshooting purposes only; not as a permanent fix to your problem.

Tools and Materials Needed:

  • Knock sensor
  • Wire cutters, if necessary
  • Screwdriver (standard or Phillips)
  • Ohm meter, if necessary
  • Piezo transducer
  • Electrical tape
  • Speaker wire

Step 1 – Preparation

Raise the hood of your car and find the knock sensor. You may need to consult your car's repair manual to locate it. Another way would be to use your ohm meter to locate the faulty wire. Set the meter to check for "continuity" and check the wires. The sensor should look like a tiny plastic donut. The actual sensor is probably attached to the engine block or firewall with a small bolt or screw through the center hole.

Step 2 – Disconnecting the Knock Sensor

After you have located the sensor, trace back the wire to see where it connects. The wire connects to the ECU (Electronic Control Unit) of your car. If the sensor is hardwired, you will have to cut the wire in two, otherwise it might have a plastic connector attached that you can simply unplug. Either way, go ahead and disconnect the sensor from the electronic circuit.

Step 3 – Bypass the Sensor

The Piezo transducer is an electronic device that vibrates as electricity is passed through it. These vibrations are translated into electricity, exactly the same way as the knock sensor.

Once you have removed the sensor, tape the Piezo transducer in a location close to the sensor. Attach one end of the wire to the positive (+) wire of the transducer. Attach the other end of the wire to the correct terminal on the ECU. This is where the repair manual comes in handy. Connect the negative (-) wire from the transducer to a chassis ground on the car.

Step 4 – Testing the Bypass

So now that you have bypassed your knock sensor, you can start the vehicle. You can now verify that the trouble code from the computer is gone.

Step 5 – Replacing the Knock Sensor

Once you have determined the knock sensor is faulty, it is fairly simple to replace. Remove the Piezo transducer and wiring you used from your troubleshooting process. Connect the positive and negative wires from the sensor to the ECU unit to any available chassis ground and attach the sensor to the engine block or firewall in place of the faulty sensor using the bolt or screw supplied.