Circuit Description

The knock sensor is fitted to the cylinder block to detect 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, ignition timing is retarded to suppress it.

Fig 1: DTC Troubleshooting Table

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

If the ECM detects above diagnosis conditions, it activates the fail-safe function where the corrective retard angle value is set to the maximum value.

Reference: INSPECTION USING OSCILLOSCOPE

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

HINT:

The correct waveforms are as shown.

Zoom in on the horizontal axis (time), and confirm that period of the wave is 80 mue sec.

(Normal mode vibration frequency of knock sensor: 12.5 kHz

HINT:

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

Fig 2: Identifying KNK Signal Wave Form