Spark

The scan tool range is -64 to +64 degrees. 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 10 degrees BTDC while operating in Bypass mode, the displayed spark advance only reflects true spark timing when the PCM has commanded IC mode.