Knock Sensor: Testing and Inspection

Knock System Circuit Check:

Knock Sensor Circuit:

Circuit Description:
The Knock Sensor (KS) is used to detect engine detonation and the PCM will retard the ignition control timing based on the signal being received. The circuitry within the knock sensor causes the PCM's 5 volts to be pulled down so that under a no knock condition CKT 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 volts DC voltage. The amplitude and frequency are dependent upon the knock level.

The PCM used with this engine contains a knock sensor module which contains the spark control logic that retards spark timing which in turn reduces detonation.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. With engine idling, there should not be a knock signal present at the PCM, because detonation is not likely under a no load condition.

2. Tapping on the engine lift hook bracket should simulate a knock signal to determine if the sensor is capable of detecting detonation. If no knock is detected, try tapping on engine block closer to sensor before replacing sensor.

3. If the engine has an internal problem which is creating a knock, the knock sensor may be responding to the internal failure.

4. This tests the integrity of the Knock Sensor (KS) module.

Diagnostic Aids:
While observing knock signal on the Tech 1 scan tool, there should be an indication that knock is present when detonation can be heard. Detonation is most likely to occur under high engine load conditions.