Charging System: Description and Operation
OVERVIEWThe 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 presented 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.
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
- Generator Lamp (if equipped)
- Check Gauges Lamp (if equipped)
- 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 from the powertrain control module (PCM) is supplied to the generator rotor to produce a magnetic field. This is done through one of the two field terminals at the rear of generator. On models of previous years, battery voltage to this field terminal was supplied from the ASD relay.
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 Diagnostic Trouble Code (DTC). The PCM will store a DTC in electronic memory for any failure it detects.
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. Once the generator begins producing sufficient current, it also provides the current needed to energize the rotor.
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.
Although the generators appear the same externally, different generators with different output ratings are used on this vehicle. Be certain that the replacement generator has the same output rating and part number as the original unit. Refer to Generator Ratings in the Specifications for amperage ratings and part numbers.
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 will be higher at colder temperatures and is gradually reduced at warmer temperatures.
Electronic Voltage Regulator
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the Powertrain Control Module (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. It then compensates and regulates generator current output accordingly.
CIRCUIT OPERATION
The charging system is an integral part of the battery and starting systems. Because all these systems work in conjunction, diagnose and test them together.
Circuit A0 from the battery connects to a bus bar in the Power Distribution Center (PDC). Circuit A11 connects to the PDC bus bar and the output terminal of the generator. A fuse in the PDC between A0 and A11 circuits protects the charging system. Circuit Z1 provides ground for the generator.
On the diesel engine applications an additional battery is used. Circuit A0 connects between the battery positive terminals of the batteries.
When the ignition switch is in either the START or RUN positions, it connects battery voltage from circuit A1 to the A21 circuit. Circuit A21 powers circuit F18 through fuse 9 in the fuse block. Circuit F18 connects to the coil side of the Automatic Shut Down (ASD) relay. Circuit A1 originates in the PDC and is connected to battery voltage. A 40 amp fuse in cavity 3 of the PDC protects the A1 circuit.
When the ASD relay energizes, it connects circuit A16 from the PDC to circuit K125. Circuit K125 splices to connect to the generator connector supplying battery voltage to the generator field.
The Powertrain Control Module (PCM) has an internal voltage regulator that controls generator output. Circuit K20 connects the generator and PCM, cavity B10. The PCM controls the generator field on the K20 circuit.
when the engine operates and there is current in the generator field, the generator produces a B+ voltage. The generator supplies B+ voltage to the battery through the A11 and A0 circuits.