The knock sensor 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 specific amount. Knock sensors contain a piezoelectric material that sends an input signal (voltage) to the PCM. As the intensity of the engine knock vibration increases, the knock sensor output voltage also increases.
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 that constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As the intensity of the crystals vibration increases, the knock sensor output voltage also increases.
The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives as an input the knock sensor voltage signal. If the signal rises above a predetermined level, the PCM will store that value in memory and retard ignition timing to reduce engine knock. If the knock sensor voltage exceeds a preset value, the PCM retards ignition timing for all cylinders. It is not a selective cylinder retard. The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, knock retard is allowed. Knock retard uses its own short-term and long-term memory program.
Long-term memory stores previous detonation information in its battery-backed RAM. The maximum authority that long term memory has over timing retard can be calibrated. Short-term memory is allowed to retard timing up to a preset amount under all operating conditions (as long as rpm is above the minimum rpm) except WOT. The PCM, using short-term memory, can respond quickly to retard timing when engine knock is detected. Short-term memory is lost any time the ignition key is turned OFF.
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 knock sensor output voltage should measure between 80mV and 4 volts with the engine running between 576 and 2208 rpm. If the output falls outside of this range, a Diagnostic Trouble Code (DTC) will set.