Charging System: Description and Operation

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.

However, when attempting to diagnose any of the systems, it is important that you keep their interdependency in mind.

The diagnostic procedures used include the most basic conventional diagnostic methods to the more sophisticated On-Board Diagnostics (OBD) built into the Powertrain Control Module (PCM). Use of a induction milliampere ammeter, Volts/Ohmmeter, battery charger, carbon pile rheostat (load tester), and 12-Volts 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 will store a DTC in electronic memory for any failure it detects. See the On-Board Diagnostics Test in Charging System for more information.

SYSTEM OPERATION
Charging System Operation
The charging system consists of:
- Generator
- Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)
- Ignition switch (refer to Ignition System for information)
- Battery (refer to Battery for information)
- Battery temperature sensor
- Generator Lamp
- Voltmeter (refer to Instrument Panel and Gauges for information)
- 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 from the ASD relay is supplied to the generator rotor and the current to produce a magnetic field is controlled by the PCM internal regulator. This is done through one of the two field terminals at the rear of generator.

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.

A battery temperature sensor, located in the battery tray housing, is used to sense battery temperature. This temperature data, along with data from monitored line Voltage, is used by the PCM to vary the battery charging rate. This is done by cycling the ground path to control the strength of the rotor magnetic field. The PCM then compensates and regulates generator current output accordingly.

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 DTC. The PCM will store a DTC in electronic memory for any failure it detects. Refer to On-Board Diagnostic Test For Charging System for more information.

Generator
The generator is belt-driven by the engine using a serpentine type drive belt. It is serviced only as a complete assembly, If the generator fails for any reason, the entire assembly must be replaced.

As the energized rotor begins to rotate within the generator, the spinning magnetic field induces a current into the windings of the stator coil.

The Y type stator winding connections deliver the induced AC current to 3 positive and 3 negative diodes for rectification. From the diodes, rectified DC current is delivered to the vehicle electrical system through the generator battery and ground terminals.

Be certain that the replacement generator has the same output rating as the original unit. See Generator Ratings in the Specifications for amperage ratings.

Noise emitting from the generator may be caused by: worn, loose or defective bearings; a loose or defective drive pulley; incorrect, worn, damaged or misadjusted fan drive belt; loose mounting bolts; a misaligned drive pulley or a defective stator or diode.

Battery Temperature Sensor
The battery temperature sensor is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line Voltage, is used by the PCM to vary the battery charging rate. System Voltage wilt be higher at colder temperatures and is gradually reduced at warmer temperatures.

The sensor is located on the inboard side of the battery tray, and makes contacts with the side of the battery.

Voltage Regulator
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a Voltage regulating circuit located within the PCM. The EVR is not serviced separately, If replacement is necessary, the PCM must be replaced.

Operation: The amount of DC current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series with the generators second rotor field terminal and its ground.

Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line Voltage and battery temperature (refer to Battery Temperature Sensor for more information). It then compensates and regulates generator current output accordingly, Also see Charging System Operation for additional information.