Knock Sensor: Testing and Inspection

Chart C-5:

Knock Sensor Circuit:

CIRCUIT DESCRIPTION:
The Knock Sensor (KS) is used to detect engine detonation and the ECM will retard the electronic spark timing based on the signal being received. The knock sensor produces an AC signal. The amplitude and frequency are dependent upon the knock level.

The PROM used with this engine contains the functions which were part of remotely mounted KS modules used on other GM vehicles. The KS portion of the PROM then sends a signal to other parts of the ECM which adjusts the spark timing to retard the spark and reduce the detonation.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. The scan tool displays knock sensor activity in counts approximately 16-22 at idle. The counts should rise when engine speed increases or falls when engine speed decreases. This step checks knock sensor activity.

2. This step checks that the internal resistance of knock sensor is within an acceptable range.

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

DIAGNOSTIC AIDS:
While observing knock signal on the 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.