Chart C-5 Knock Sensor (KS) System Check

Chart C-5:

Knock Sensor Circuit:

CIRCUIT DESCRIPTION
The knock sensor system is used to detect engine detonation. The Engine Control Module (ECM) will retard the spark timing based on a signal being received from the knock sensor. The knock sensor produces an Alternating Current (AC) voltage which is sent to the ECM. The amount of AC voltage produced by the sensor is determined by the amount of knock. The circuitry within the knock sensor cause the ECMs 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 2.3 volts.

TEST DESCRIPTION
Numbers below refer to circled numbers 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 engine 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 test determines if the knock sensor is faulty or Programmable Read Only Memory (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 Tech 1 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.