Code 43, Electronic Spark Control (4.3L Turbo & Models With 4L80-E Transmission)

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ECM/PCM applies and monitors a 5-volt DC signal to knock sensor. Internal knock sensor circuitry pulls this DC signal down to about 2.5 volts. When knock sensor detects detonation, it generates an AC signal which rides back on DC signal to ECM/PCM. Knock signal intensity is dependent upon knock signal level.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Code 43 will set when vehicle reaches normal operating temperature (but not overheating), high engine load is indicated by MAP sensor and voltage on circuit No. 496 is greater than 3.5 volts DC or less than 1.5 volts DC. This step determines if system is functioning properly at current time.
This step determines state of 5-volt reference signal applied to sensor.
Checks knock sensor internal resistance.

CODE 43 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Application		ECM Terminal	Wire Color
All With 4L80-E
Knock Signal		D5	Dark Blue

Fig 1: Code 43, Schematic, Electronic Spark Control

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 43, Flow Chart, Electronic Spark Control

Courtesy of GENERAL MOTORS CORP.