Electronic Spark Control Module: Description and Operation

Fig. 10 Knock control unit. 2.2L/4-133 turbocharged engine:

When vibration in the engine occurs, voltage is generated by the knock sensor and signal is sent through the knock control unit (KCU), Fig. 10, and to the electronic control assembly. The KCU acts as a signal filter which only allows the knocking signals considered to be above normal engine vibrations to reach the ECA. The ECA will then retard ignition timing and reduce turbocharger boost pressure accordingly.