Generator Field Sense

The PCM regulates the the charging system voltage within a range of 12.9 to 15.0 volts. It also controls ASD relay operation. The input for the ASD relay comes from the engine speed sensor through the controller. When the engine running speed is above 384 rpm, a signal is sent from the PCM to engage the ASD relay, which supplies generator field control. When rpm drops below 320, the signal to the ASD relay is dropped, opening the generator field circuit.