Knock Sensor: Testing and Inspection

Chart C-5 Knock Sensor System Check:

Knock Sensor System Wiring Diagram:

Circuit Description:

The knock sensor system is used to detect engine detonation. The ECM will retard the spark timing based on a signal being received from the knock sensor. The knock sensor produces an AC voltage which is sent to the ECM. The amount of AC voltage produced by the sensor is determined by the amount of engine knock. The circuitry within the knock sensor causes the ECM's 5 volts to be pulled down so that under a no engine knock condition, CKT 496 would measure about 2.5 volts.

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 ECM, because detonation is not likely under a no load condition.

2. Tapping on the engines right exhaust manifold 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 a 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 test determines if the knock sensor is faulty or if the KS portion of the PROM is faulty. If it is determined that the PROM is faulty, be sure that it is properly installed and latched into place. If not properly installed, repair and retest.


Diagnostic Aids:

While observing knock signal on the scanner, 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.