All the vehicles with 4-cylinder engines are equipped with a knock sensor, which is threaded into the side of the cylinder block, in front of the starter. When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount.
Knock sensors contain a piezoelectric material which sends an input voltage (signal) to the PCM. As the intensity of the engine knock vibration increases, the knock sensor output voltage also increases.
See Figures 1 and 2
Visually check the connector, making sure it is attached properly and that all of the terminals are straight, tight and free of corrosion.
A number of factors affect the engine knock sensor. A few of these are: ignition timing, cylinder pressure, fuel octane, etc. The knock sensor produces an AC voltage whose amplitude increases with the amount of engine knock. The knock sensor can be tested with a digital voltmeter. The RMS voltage is produced at about 20mVac (at about 700 rpm) and increases to about 600mVac (5000 rpm). If the output falls outside of this range, a Diagnostic Trouble Code (DTC) will set.
REMOVAL & INSTALLATION
See Figure 3
- Disconnect the negative battery cable.
- Unplug the electrical connector from the knock sensor, which is located on the engine block, in front of the starter.
- Use a crow's foot wrench to remove the knock sensor from the vehicle.
- Install the sensor in the vehicle and tighten to 7 ft. lbs. (10 Nm). Make sure not to over or under-tighten the sensor, as is could adversely affect knock sensor performance, causing improper spark control.
- Attach the knock sensor electrical connector.
- Connect the negative battery cable.