Alternator: Description and Operation

GENERATOR




The ECM controls generator charging by supplying 12 volts on the generator L-terminal circuit whenever the ignition is turned On or the engine is running. This control voltage is necessary for the generator to charge once the generator begins to spin. With the ignition On, engine Off, the generator will ground the generator L-terminal circuit through a resistor. When the engine is started and the generator begins to charge, the generator will open the circuit (still using the 12 volt control voltage) signaling to the ECM that the generator is charging.

CHARGE TELLTALE If the voltage at the ECM generator L-terminal is low when the engine is running, the ECM will send a message to the BCM over the CAN link, who will send a message to the I/P cluster over the Class II link to turn On the Charge telltale.