Generator "L" Light Circuit

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) controls generator charging by supplying a voltage (5 volts or 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 switch in RUN position, 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 control voltage) signaling to the ECM that the generator is charging. If the voltage at the PCM generator "L" terminal is low when the engine is running, the PCM will send a message to the instrument panel cluster to turn on the charge telltale.