Knock Sensor: Testing and Inspection

Electronic Spark Control (ESC) Circuit Check:

Electronic Spark Control (ESC) Circuit:

Circuit Description:
The Code 43 circuit consists of two knock sensors with one wire that goes directly to the ECM. There are two Code 43 checks performed by the ECM. One check consists of monitoring CKT 496 for a voltage that is more than .63 volt and less than 4.4 volts.

If voltage is either too high or too low for 2 or more seconds, Code 43 will set. Once engine temperature reaches 85°C, MAP is over 83 kPa, and engine speed is less than 3800 rpm, the ECM will perform a self check. This self check will advance the timing until it receives a knock signal. If no knock signal is received, Code 43 will set.

Diagnostic Aids:
The ECM applies 5 volts to CKT 496. A 8200 ohm resistor in the knock sensors 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 ECM, is able to read this signal as knock and incrementally retard spark.

If the ESC system checks OK, but detonation is the complaint, Detonation/Spark Knock/Pings