System Diagnosis - Electronic Spark Control (ESC) - With 4L80-E

Electronic Spark Control (ESC) Circuit Check:

Electronic Spark Control (ESC) Circuit:

Circuit Description:
The Code 43 circuit consists of a knock sensor with one wire that goes directly to the PCM. There are two Code 43 checks performed by the PCM. One check consists of monitoring CKT 496 for a voltage that is more than .04 volt and less than 4.6 volts.

If voltage is either too high or too low for 16 or more seconds, Code 43 will set. Once engine temperature reaches 87.5°C, MAP is over 81 kPa, and engine speed is less than 3200 rpm, the PCM will perform a self check. This self check will advance the timing until it receives a knock signal. If no knock signal is received during two consecutive tests, Code 43 will set.

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.

1. The first test is to determine if thew 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 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 PCM, is able to read this signal as knock and incrementally retard spark.

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