Ignition Mode

The scan tool displays BYPASS or IC. This indicates the commanded state of the bypass signal output from the PCM. If BYPASS is displayed, the Ignition Control Module (ICM) is controlling the spark advance at a fixed 10 degrees before Top Dead Center (BTDC). An IC displayed indicates that the PCM has requested control of the spark advance. The ICM determines the correct operating mode based on the level of voltage that the PCM applies to the ignition control module bypass circuit. The PCM provides 5 volts to the ICM bypass circuit if conditions are appropriate for PCM control of spark timing. If the PCM does not apply 5 volts to the bypass circuit, or if the ICM does not receive the signal, the module will control spark timing.