Voltage Signal: Description and Operation

PURPOSE
The Alternator FR Signal is an Idle Control System input signal to the Engine Control Module (ECM). The ECM uses it as a confirmation of current output rate of the alternator. The ECM Uses the information to calculate the load placed on the engine by the alternator and adjusts the Idle Air Control Valve (IAC) accordingly to maintain a steady idle speed. This signal differs from the Electrical Load Detector (ELD) signal, which the ECM monitors to adjust the charge rate, in that it is a feedback signal by which the ECM confirms that charging is actually occurring.