Code 43: Elect Spark Control: Notes

The knock sensor is used to detect engine detonation and the ECM will retard the electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM 5-volt reference to be pulled down so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on this DC signal provided by the ECM. The knock amplitude and signal frequency is dependent upon the knock level. If circuit No. 496 becomes open or shorted to ground, the voltage will either go to greater than 3.5 volts or less than 1.5 volts. If either condition occurs, Code 43 will be stored. On W body vehicles, ECM will also advance timing under certain load and engine speed conditions (3400-4400 RPM) to test knock sensor operation. If test is run and no knock signal is produced, Code 43 will set.

1. Determines if conditions for Code 43 exist (voltage on circuit No. 496 greater than 3.5 volts or less than 1.5 volts). The system is designed to retard spark up to 17 degrees if either condition exists.
2. The ECM applies and monitors 5 volts on circuit No. 496. This voltage should be present at the knock sensor terminal.
3. Determines if knock sensor resistance is between 3300-4500 ohms, sensor is okay.