Electronic Spark Control Module: Description and Operation

Varying octane levels in today's gasoline can cause detonation in engines. Detonation is sometimes called spark knock.

To control spark knock an Electronic Spark Control (ESC) system has been added. This system is designed to retard spark timing up to 20~ to reduce spark knock in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.




The ESC system has three major components:
^ ESC module
^ ESC knock sensor
^ ECM

The ESC knock sensor detects abnormal vibration (spark knocking) in the engine. The sensor is mounted in the engine block near the cylinders. The ESC module receives the knock sensor information and sends a signal to the ECM. The ECM then adjusts the timing to reduce spark knocking.

The ESC module sends a voltage signal (8 to 10 volts) to the ECM when no spark knocking is detected by the ESC knock sensor, and the ECM provides normal spark advance.

When the knock sensor detects spark knock, the module turns "OFF" the circuit to the ECM. The ECM then retards EST to reduce spark knock.

Loss of the ESC knock sensor signal or loss of ground at ESC module would cause the signal to the ECM to remain high. This condition would cause the ECM to control EST as if no spark knock were happening. No retard would occur, and spark knocking could become severe under heavy engine load conditions, possibly leading to pre-ignition and severe engine damage.


Loss of the ESC signal to the ECM would cause the ECM to constantly retard EST. This could result in sluggish performance and cause a Code 43 to set. Spark retard without the knock sensor connected could indicate a noise signal on the wire to the ESC module or a malfunctioning ESC module.