The knock sensors (KS) job, is to monitor the engine, for any signs of detonation.

Consequently, detonation is the premature ignition, of the air fuel mixture.

Detonation is a sound that occurs, when there is a second unplanned ignition within a cylinder. However, it is separate, from the regular controlled ignition from a spark plug.

Knock sensors (KS) monitor this frequency, because the second ignition, creates a second flame front. Consequently, when those two reactions collide, you get a knock. Detonation produces, a sharp, mechanical knocking sound. But, is usually detected, at higher engine speeds or a sudden, increase in engine load.

So, to prevent detonation, knock sensors, monitor the frequency, at which normal detonation occurs. Consequently, giving the (PCM), continuous live stream data, that allows the (PCM), to control the ignition timing.

Then, to improve engine efficiency, the (PCM) keeps the ignition timing, as far advanced as possible. Based on the current operating conditions, such as, engine speed, load, throttle position, and vehicle speed.

So, if the knock sensors detect, a change in that frequency, it will generate a new signal voltage. Consequently, that signal voltage, is based on the changed frequency. Which the (PCM) then interprets, as detonation.

So, to correct this condition, the (PCM) then, retards the ignition timing. But, only when the detonation frequency, matches a wave amplitude that is based on, a pre-programmed value.

So, the advantage of this is, that the (PCM), can always keep the ignition timing advanced. Therefore, suitable for any given set of engine operating conditions. As a result, adding to engine efficiency and fuel economy, while lowering emissions. In other words, defective knock sensors, have a direct bearing on engine operation and efficiency.

Symptoms Of A Bad Knock (KS) Sensor Include:

  • A failed knock sensor will register a trouble code and turn on the Check Engine lamp (CEL).
  • But, some engines will require, multiple failure cycles, before storing a code.  (P0325)
  • Engine Misfires.
  • Vibration, especially at highway speed.
  • Thumping or knocking noise, from the engine.
  • Poor fuel economy and acceleration.

Knock sensors don’t fail often, but if you suspect this problem, it’s one you need to check out quickly.

Choose Your  Knock Sensors Help Topic Below

Engine Spark Knock – That Annoying Knocking, Pinging Or Rattling Sound

Engine Knocking – Pinging – Rattling Noise – Common Causes

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