C 2500 Suburban 2WD V8-350 5.7L (1994)
KS Circuit (Single Knock Sensor)
Circuit Description:
The Knock Sensor (KS) system consist of a knock sensor with one wire that goes directly to the PCM. There is a check performed by the PCM. The
check consist of monitoring CKT 496 for a voltage that is more than .04 volt and less than 4.6 volts.
If the voltage is either too high or too low for 16 or more seconds, DTC 43 will set.
Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
1. The first test is to determine if the system is functioning at the present time.
2. Test two determines the state of the 5 volt reference voltage applied to the knock sensor circuit.
Diagnostic Aids: The PCM applies 5 volts to CKT 496. A 3900 ohm resistor in the knock sensor reduces the voltage to about 2.5 volts. When knock
occurs, the knock sensor produces a small AC voltage that rides on top of the 2.5 volts already applied. An AC voltage monitor, in the PCM, is able to
read this signal as knock and incrementally retard spark.
If the KS system checks OK, but detonation is the complaint, refer to DIAGNOSIS BY SYMPTOM/ DETONATION/SPARK KNOCK/PINGS See:
Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic Procedures/Detonation/ Spark Knock.
