Charging System: Description and Operation

Charging System Schematic - Typical:

OVERVIEW
The battery, starting, and charging systems operate with one another, and must be tested as a complete system. In order for the vehicle to start and charge properly, all of the components involved in these systems must perform within specifications.

When attempting to diagnose any of these systems, it is important that you keep their interdependency in mind. The diagnostic procedures used in these groups include the most basic conventional diagnostic methods to the more sophisticated On-Board Diagnostics (OBD) built into the Powertrain Control Module (PCM). Use of an induction ammeter, Volt/ohmmeter battery charger, carbon pile rheostat (load tester), and 12-Volt test lamp may be required.

All OBD-sensed systems are monitored by the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC). The PCM wilt store a DTC in electronic memory for any failure it detects. See the On-Board Diagnostics Test - Charging System for more information.

SYSTEM OPERATION
The charging system consists of:
- Generator
- Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM).
- Ignition switch
- Battery
- Battery temperature sensor
- Voltmeter
- Wiring harness and connections

The charging system is turned on and off with the ignition switch. When the ignition switch is turned to the ON position, battery Voltage is applied to the generator rotor through one of the two field terminals to produce a magnetic field. The generator is driven by the engine through a serpentine belt and pulley arrangement.

The amount of DC current produced by the generator is controlled by the EVR (field control) circuitry, contained within the PCM. This circuitry is connected in series with the second rotor field terminal and ground.

All vehicles are equipped with On-Board Diagnostics (OBD). All OBD-sensed systems, including the EVR (field control) circuitry, are monitored by the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC). The PCM will store a DTC in electronic memory for any failure it detects. See On-Board Diagnostic System Test for more information.

CIRCUIT OPERATION
The charging system is an integral part of the battery and starter systems. Since these systems work together, any diagnosis and testing should be done in conjunction.

The charging system is protected by a 10 gauge fusible link located in the A11 circuit. The A11 circuit is connected to the battery feed bus bar of the Power Distribution Center (PDC) and the generator.

The generator is case-grounded through its attaching bracket. This generator uses a voltage regulator internal to the Powertrain Control Module (PCM).

When the vehicle is running, battery voltage is applied to the generator field terminal through the A142 circuit, on all engine applications. This circuit is controlled by the contact side of the Automatic Shut-Down (ASD) relay. The ground, or voltage regulated side, of the generator field is controlled by the K20 circuit. Circuit K20 connects to cavity 4 of the PCM.

When there is current present in the field, and the rotor is turning, the stator in the generator produces a B+ voltage that is supplied to the battery through the A11 and A0 circuits. The A11 circuit is connected to the output terminal of the generator and the battery feed bus bar of the PDC. The A0 circuit is a direct battery feed from the battery to the PDC.

Grounding for the system is accomplished at the battery negative terminal. These grounds go to the engine and body.