Spark

The scan tool range is -64 degrees to 64 degrees. This displays the spark timing being commanded by the PCM on the IC circuit. A negative (-) value indicates degrees before top dead center (BTDC) or spark advance. A positive value indicates degrees after top dead center (ATDC) or spark retard. Because the ignition control module sets spark advance at a fixed value of 100 BTDC while operating in Bypass mode, the displayed Spark advance only reflects the true spark timing when the PCM has commanded IC mode.