Loss of the ESC knock sensor signal or loss of ground at the ESC module would cause the signal to the ECM to remain high. This condition would cause the ECM to control EST as if there was no spark knock. No retard would occur and spark knocking could become severe under heavy engine load.
Spark retard without the knock sensor connected could indicate a noise signal on the wire to the ECM or a malfunctioning ESC module.
Loss of the ESC signal to the ECM would cause the ECM to constantly retard the EST. This could result in sluggish performance and cause a Code 43 to set. Code 43 indicates that the ECM is receiving less than 6 volts for a 4 second period with the engine running. For more information concerning codes and the self-diagnostic system, please refer to Emission Controls of this guide.