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DR
CHARGING
. . . . . . . . . . . . . . . . . . . . . . . . . 19
OPERATION
. . . . . . . . . . . . . . . . . . . . . . . . . . . 19
DIAGNOSIS AND TESTING - CHARGING
SYSTEM
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
GENERATOR RATINGS
/ CHARGING SYSTEM . . . . . . . . . . . . . . . . . . 20
. . . . . . . . . . . . . . . . . . . . . . . . . 21
CHARGING
DESCRIPTION
The charging system consists of:
• Generator
• Electronic Voltage Regulator (EVR) circuitry
within the Powertrain Control Module (PCM). Elec-
tronic Control Module (ECM) for diesel engines.
• Ignition switch
• Battery (refer to 8, Battery for information)
• Battery temperature sensor
• Check Gauges Lamp (if equipped)
• Voltmeter (refer to 8, Instrument Panel and
Gauges for information)
• Wiring harness and connections (refer to 8, Wir-
ing Diagrams for information)
OPERATION
The charging system is turned on and off with the
ignition switch. The system is on when the engine is
running and the ASD relay is energized. When the
ASD relay is on, voltage is supplied to the ASD relay
sense circuit at the PCM (ECM Diesel). This voltage
is connected through the PCM (ECM Diesel) and sup-
plied to one of the generator field terminals (Gen.
Source +) at the back of the generator.
The amount of direct current produced by the gen-
erator is controlled by the EVR (field control) cir-
cuitry contained within the PCM (ECM Diesel). This
circuitry is connected in series with the second rotor
field terminal and ground.
A battery temperature sensor, located in the bat-
tery tray housing, is used to sense battery tempera-
ture. This temperature data, along with data from
monitored line voltage, is used by the PCM (ECM
Diesel) to vary the battery charging rate. This is
CHARGING
TABLE OF CONTENTS
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REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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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 Diagnos-
tics (OBD). All OBD-sensed systems, including EVR
(field control) circuitry, are monitored by the PCM
(ECM Diesel). Each monitored circuit is assigned a
Diagnostic Trouble Code (DTC). The PCM will store a
DTC in electronic memory for certain failures it
detects.
The Check Gauges Lamp (if equipped) monitors:
charging system voltage, engine coolant tempera-
ture and engine oil pressure. If an extreme condition
is indicated, the lamp will be illuminated. This is
done as reminder to check the three gauges. The sig-
nal to activate the lamp is sent via the CCD bus cir-
cuits. The lamp is located on the instrument panel.
Refer to 8, Instrument Panel and Gauges for addi-
tional information.
DIAGNOSIS AND TESTING - CHARGING
SYSTEM
The following procedures may be used to diagnose
the charging system if:
• the check gauges lamp (if equipped) is illumi-
nated with the engine running
• the voltmeter (if equipped) does not register
properly
• an undercharged or overcharged battery condi-
tion occurs.
Remember that an undercharged battery is often
caused by:
• accessories being left on with the engine not
running
CHARGING
8F - 19
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