Jeep Cherokee (XJ): Description and operation
DESCRIPTION The charging system consists of: 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. This voltage is connected
through the PCM and supplied to one of the generator
field terminals (Gen. Source +) at the back of the
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 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 certain failures it detects. Refer to
On-Board Diagnostics in Group 25, Emission Control
System for more DTC information.
The Check Gauges Lamp (if equipped) monitors:
charging system voltage, engine coolant temperature
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 signal
to activate the lamp is sent via the CCD bus circuits.
The lamp is located on the instrument panel.
Refer to Group 8E, Instrument Panel and Gauges for
additional information. DESCRIPTION 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. OPERATION 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 terminal.
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 section at the
back of this group 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. DESCRIPTION The Battery Temperature Sensor (BTS) is attached
to the battery tray located under the battery. OPERATION The BTS 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.
The PCM sends 5 volts to the sensor and is
grounded through the sensor return line. As temperature
increases, resistance in the sensor decreases
and the detection voltage at the PCM increases.
The BTS is also used for OBD II diagnostics. Certain
faults and OBD II monitors are either enabled
or disabled, depending upon BTS input (for example,
disable purge and enable Leak Detection Pump
(LDP) and O2 sensor heater tests). Most OBD II
monitors are disabled below 20F. DESCRIPTION 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 (B+) and
battery temperature (refer to Battery Temperature
Sensor for more information). It then determines a
target charging voltage. If sensed battery voltage is
0.5 volts or lower than the target voltage, the PCM
grounds the field winding until sensed battery voltage
is 0.5 volts above target voltage. A circuit in the
PCM cycles the ground side of the generator field up
to 100 times per second (100Hz), but has the capability
to ground the field control wire 100% of the time
(full field) to achieve the target voltage. If the charging
rate cannot be monitored (limp-in), a duty cycle
of 25% is used by the PCM in order to have some
generator output. Also refer to Charging System
Operation for additional information.Charging system
Generator
Battery temperature sensor
Electronic voltage regulator
Other materials:
Safety precautions
SAFETY PRECAUTIONS AND WARNINGS
DESCRIPTION
WARNING: USE A OSHA APPROVED BREATHING
FILTER WHEN SPRAYING PAINT OR SOLVENTS IN
A CONFINED AREA. PERSONAL INJURY CAN
RESULT.
AVOID PROLONGED SKIN CONTACT WITH
PETROLEUM OR ALCOHOL - BASED CLEANING
SOLVENTS. PERSONAL INJURY CAN RESULT.
DO NOT ...