Circuit Description

The knock sensor is fitted on the cylinder block to detect the engine knocking. This sensor contains a piezoelectric element which generates a voltage when it becomes deformed, which occurs when the cylinder block vibrates due to knocking. If engine knocking occurs, the ignition timing is delayed to suppress it.

Fig 1: DTC Detection Condition Table

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

If the ECM detects the DTC "P0325", it enters the fail-safe mode in which the corrective retarded angle value.

Reference: INSPECTION USING OSCILLOSCOPE

With the engine racing (4,000 RPM) measure waveform between terminal KNK of the ECM connector and body ground.
HINT:

The correct waveforms are as shown.
Spread the time on the horizontal axis, and confirm that period of the wave is 132 mu sec.
(Normal mode vibration frequency of knock sensor: 7.6 kHz)

HINT:

If normal mode vibration frequency is not 7.6 kHz, the sensor is malfunctioning.

Fig 2: Identifying Knock Sensor 1 Circuit Description