[Front Range]

This might help.

CODE 43

Trouble Code 43 indicates that there may be a malfunction in the Electronic Spark Control (ESC) circuit. ESC is used to sense spark knock (pinging) and retard the timing to eliminate it. The knock sensor is located at the rear of the engine block. The ECM will retard the timing by as much as 20 degrees in 1 degree increments. A loss of knock sensor signal or loss of ground at the ESC module will cause the signal at the ECM to remain high. The ECM will act as if no knock is present, and may possibly result in engine damage, due to detonation.

Code 43 is set when:
1. Voltage at Knock Sensor is above 4.8 volts or below .64 volts.
2. Either condition is met for about 10 seconds.

Possible causes:
1. Open or shorted knock sensor
2. Loose knock sensor
3. Excessive mechanical noise within engine
4. Improper or incorrectly installed MEM-CAL in the ECM or defective ECM
5. Intermittent open in the EST line to the ignition module