With 4L80 Automatic Transmission

ELECTRONIC SPARK CONTROL (ESC) CIRCUIT
ALL VEHICLES WITH 4L80-E TRANSMISSION

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 4.16 volts and less than 0.64 volt.
- If voltage is either too high or too low, for 26 or more seconds, Code 43 will set. Once engine temperature reaches 87°C or more, but not over 104°C, and MAP and engine speed are below 81 kPa and 3200 rpm respectively, the PCM will perform a self check by advancing the timing incrementally while anticipating a knock signal. If no knock signal is received during two consecutive tests, Code 43 will be set.

Test Description:

NOTE:
- 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 3500 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.

For further information, refer to "Driveability Symptoms," for "PCM/ECM Intermittent Codes or Performance."