Starting and Charging Circuit. Cadillac Concours 1996

For 1990-2009 cars

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

The instrument panel cluster (IPC) initiates generator operation by supplying 12 volts, through an internal resistor, to the generator L terminal over RED (225). The generator voltage regulator in turn applies voltage to the rotor in the form of a PWM (Pulse Width Modulated) signal that energizes the field windings.

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

Vehicles with the heated windshield option (C50) are equipped with a generator that has three insulated leads next to the output terminal. These leads provide three-phase AC power directly to the heated windshield power module. On vehicles equipped with this option, the stator is connected directly to the three output terminals on the back of the generator.

Generator F Terminal

The F terminal is connected internally to the voltage regulator and externally to the powertrain control module (PCM). The PCM monitors the field voltage on the generator F terminal. If the field voltage duty cycle on the terminal is low, the PCM sets Diagnostic Trouble Code (DTC) P1638.

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 after the engine is running. Through an internal resistor, the IPC sends out 12 volts on RED (225), allowing the generator to turn ON. (If the wire to the L terminal is open or grounded, the generator will not operate.) Once the generator turns ON, the regulator is supplied with voltage from the output stud. 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 conditions:

• | A shorted output diode

• | A malfunctioning regulator

• | An open or shorted rotor

• | Voltage that is too high or too low

• | A shaft that is not rotating

The IPC will, in turn, sense the L terminal ground. The IPC then displays the BATTERY NO CHARGE message on the driver information center. For export vehicles, the IPC will also display the VOLTS message.

The IPC also monitors system voltage and sets codes for voltage that is too high or too low.

When the ignition switch is turned to the START position and the gear selector is in PARK or NEUTRAL, battery voltage is supplied to the starter enable relay coil along the following pathway:

1. From the BATT 2 fuse
2. Through RED (342)
3. To the ignition switch
4. To YEL (5)
5. To the PARK/NEUTRAL position switch
6. To (YEL 1737)
7. To the starter enable relay coil

At the same time, a start request is sent by the PASS-Key® II input to the instrument panel cluster (IPC).If the IPC senses correct Pass-Key® II system resistance, the IPC then energizes the starter enable relay by grounding one side of the relay coil. (Refer to Section 8A-133 for PASS-Key® II circuit description.)

Once the starter enable relay is energized, the normally open contacts close, completing the following circuit:

• | From the BATT1 fuse

• | Through RED (142)

• | To the closed relay contacts

• | To PPL (6)

• | To the starter solenoid

Completing the starter solenoid circuit energizes both the hold-in and the pull-in windings. The circuit through the pull-in winding is completed to ground through the starter motor. The windings work together magnetically to hold and pull in the plunger. The plunger moves the shift lever. This action causes the starter drive assembly to rotate as it engages with the flywheel ring gear on the engine. The plunger rotates at the same time. The plunger rotation closes the solenoid switch contacts in the starter solenoid. Full battery voltage is applied directly to the starter motor, and the starter motor cranks the engine.

As soon as the solenoid switch contacts close, current stops flowing through the pull-in winding. This happens because battery voltage is applied to both ends of the windings. The hold-in winding remains energized. Its magnetic field is strong enough to hold the plunger, the shift lever, and the starter drive assembly solenoid switch contacts in place to continue cranking the engine.

Starter and Charging System

Releasing the ignition switch from the START position removes battery voltage from PPL (6) and from the junction of the two starter windings. Current flows from the motor contacts through both windings to ground at the end of the hold-in winding. However, the direction of current flow through the pull-in winding is now opposite the direction of current flow when the winding was first energized.

The magnetic fields of the pull-in and hold-in windings now oppose one another. This action of the windings, along with the help of the return spring, causes the starter drive assembly to disengage and the solenoid switch contacts to open simultaneously. As soon as the contacts open, the starter circuit turns off.

Starter Inhibit Operation

The Northstar powertrain has a starter inhibit function that prevents engagement of the starter once the engine is running. The starter inhibit function operates in the following manner:

1. The PCM checks for an engine RPM signal that is greater than engine cranking speed.
2. Once the engine is running, the PCM sends the starter inhibit Class II signal to the instrument panel cluster.
3. This signal opens the starter enable relay control.
4. The starter enable relay control is prevented from closing, causing any ignition key input to be ignored.

This prevents the starter from engaging while the engine is running.