Charging

The basic charging system consists of a generator with an internal voltage regulator. The generator supplies DC voltage to operate the vehicle's electrical system and to charge the battery.

The regulator provides current to the generator's rotor. Current flowing through the rotor creates a magnetic field. The field rotates as the engine drives the rotor, creating an AC voltage in three stator windings in the generator. AC voltage is changed to DC voltage by the rectifier bridge. This DC output is applied to the battery and the vehicle circuits at the BAT terminal of the generator.

The IPC initiates generator operation by supplying 12 volts, through an internal resistor, to the generator "L" terminal over CKT 225 (RED). The generator regulator in turn applies voltage to the rotor as a Pulse Width Modulated (PWM) signal to energize the field windings.

When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width, regulating the generator output voltage. The regulator controls the charging system voltage and therefore the ampere rate of battery charge and power supplied to the vehicle.

Generator F Terminal
The "F" terminal is connected internally to the voltage regulator and externally to the PCM. The PCM monitors the field voltage on the generator "F" terminal. If field voltage duty cycle on the terminal is low, the PCM sets DTC P1638. (Refer to Battery Message Diagnosis.) Preliminary Diagnosis - Battery Message

Generator L Terminal
The "L" (lamp) terminal is connected internally to the voltage regulator and externally to the instrument panel cluster (IPC). The "L" terminal is used to turn on the generator and to monitor generator operation. The "L" terminal enables generator operation only alter the engine is running. Through an internal resistor, the IPC sends out 12 volts on CKT 225 (RED) to allow the generator to turn "ON." (If the wire to the "L" terminal is open or grounded, the generator does not turn on.) Once the generator turns "ON," the regulator receives its supply voltage from the output stud and the generator is then self-energizing.

The "L" terminal is also used by the generator to indicate internal faults. The regulator grounds the "L" terminal when it detects an internal problem. The regulator can detect any of the following: a shorted output diode, malfunctioning regulator, an open or shorted rotor, an under- or over-voltage condition, or shaft not rotating. The IPC senses this ground and displays the BATTERY NO CHARGE message on the driver information center. For export vehicles, the VOLTS telltale also lights on the IPC.

The IPC also monitors system voltage and sets codes for under- or over-voltage conditions. (Refer to Battery Message Diagnosis.) Preliminary Diagnosis - Battery Message