Charging system – general information and precautions
The charging system consists of the alternator; the Electronic Voltage Regulator (EVR), the ignition switch, the battery, a battery temperature sensor, a voltage gauge, a charge indicator light and the wiring between all the components. The charging system supplies electrical power for the ignition system, the lights, the radio, etc. The alternator is driven by a serpentine drivebelt at the front of the engine.
The ignition switch turns the charging system on and off. The system remains on as long as the engine is running and the Automatic Shut Down (ASD) relay is energized. When the ASD relay is on, voltage is supplied to the ASD relay sense circuit at the PCM (gasoline engines) or the ECM (diesel engines). This voltage is connected through the PCM/ECM and supplied to the alternator field terminal (GEN SOURCE +) on the backside of the alternator. The EVR’s field control circuit inside the PCM/ECM regulates the current output of the alternator (there is no external voltage regulator). The field control circuit is connected in series with the second rotor field terminal and ground.
The battery temperature sensor, which is mounted on the underside of the battery tray, is a Negative Temperature Coefficient (NTC) thermistor that receives a 5-volt signal from the PCM/ECM and is grounded through a return wire. As the temperature of the battery increases, the resistance in the temperature sensor decreases and the detection voltage at the PCM/ECM increases. The PCM/ECM uses the signal from the battery temperature sensor and data from monitored line voltage to vary the battery charging rate. It does so by cycling the alternator’s ground path, which controls the strength of the rotor’s magnetic field. The PCM/ECM regulates the alternator’s current output accordingly. System voltage is higher when the engine is cold and is gradually reduced to a lower voltage as the temperature increases. To replace the battery temperature sensor, refer to Chapter Emissions and engine control systems.
When the engine is running, the voltage gauge on the instrument cluster indicates electrical system voltage. The indicator needle should be within the normal range if the battery is charged. If the needle moves outside the normal range and stays there during normal driving, inspect the charging system (Charging system – check). If the voltage gauge is defective, replace the instrument cluster (see Chassis electrical system). The voltage gauge cannot be serviced separately from the cluster.
On some models a CHECK GAUGES indicator light, which is located on the instrument cluster, illuminates when the voltage gauge, the oil pressure gauge or the engine coolant gauge indicates a reading that is either too high or too low. If this happens, the system being monitored by the gauge that’s out of range requires immediate attention.
The charging system doesn’t ordinarily require periodic maintenance. However, you should inspect the drivebelt, the battery, the charging system wiring harness and all connections at the intervals outlined in Chapter Tune-up and routine maintenance. Be very careful when making electrical circuit connections to the alternator or the charging system circuit and note the following:
a) When reconnecting wires to the alternator from the battery, be sure to note the polarity.
b) Before using arc-welding equipment to repair any part of the vehicle, disconnect the wires from the alternator and the battery terminals.
c) Never start the engine with a battery charger connected.
d) Always disconnect both battery cables before using a battery charger.
e) The alternator is turned by an engine drivebelt, which could cause serious injury if your hands, hair or clothes become entangled in it with the engine running.
f) Because the alternator is connected directly to the battery, it could arc or cause a fire if overloaded or shorted out.
g) Wrap a plastic bag over the alternator and secure it with rubber bands before steam-cleaning the engine.