Jeep XJ. Manual — part 354
The battery input also provides the voltage that is
needed to keep the PCM memory alive. The memory
stores Diagnostic Trouble Code (DTC) messages.
Trouble codes will still be stored even if the battary
voltage is lost.
SENSOR RETURN—ECM/PCM INPUT (ANALOG
GROUND)
DESCRIPTION
Sensor Return provides a low noise Analog ground
reference for all system sensors.
IGNITION CIRCUIT SENSE—ECM/PCM INPUT
DESCRIPTION
The ignition circuit sense input signals the ECM
and PCM that the ignition (key) switch has been
turned to the ON position. This signal initiates the
glow plug control routine to begin the “pre–heat”
cycle.
IGNITION CIRCUIT SENSE—PCM INPUT
The ignition circuit sense input signals the PCM
that the ignition (key) switch has been turned to the
ON position. This signal initiates the glow plug con-
trol routine to begin the “pre–heat” cycle.
POWER GROUND
DESCRIPTION
Provides a common ground for power devices (sole-
noid and relay devices).
NEEDLE MOVEMENT OR INTRUMENTED FIRST
INJECTOR—ECM INPUT
DESCRIPTION
This input from the ECM supplies a constant 30
mA electrical current source for the first injector sen-
sor. It will vary the voltage to this sensor when it
senses a mechanical movement within the injector
needle (pintle) of the number–1 cylinder fuel injector.
When this voltage has been determined by the ECM,
it will then control an output to the fuel timing sole-
noid (the fuel timing solenoid is located on the fuel
injection pump). Also refer to Fuel Injection Pump for
additional information.
The first injector sensor is a magnetic (inductive)
type.
The first injector sensor is used only on the fuel
injector for the number–1 cylinder (Fig. 4). It is not
used on the injectors for cylinders number 2, 3, or 4.
FUEL INJECTOR SENSOR—GROUND
DESCRIPTION
Provides a low noise ground for the fuel injector
sensor only.
ENGINE COOLANT TEMPERATURE SENSOR—
ECM/PCM INPUT
DESCRIPTION
The 0–5 volt input from this sensor tells the ECM
and PCM the temperature of the engine coolant.
Based on the voltage received at the ECM, it will
then determine operation of the fuel timing solenoid,
glow plug relay, electrical vacuum modulator (emis-
sion component) and generator (charging system).
The sensor is located on the side of the #3 cylinder
head near the rear of fuel injection pump (Fig. 5).
ENGINE SPEED SENSOR—ECM INPUT
DESCRIPTION
The engine speed sensor is mounted to the trans-
mission bellhousing at the left/rear side of the engine
block (Fig. 6).
The engine speed sensor produces its own output
signal. If this signal is not received, the ECM will not
allow the engine to start.
The engine speed sensor input is used in conjunc-
tion with the first injector sensor to establish fuel
injection pump timing.
Fig. 4 Fuel Injector Sensor
1 – NEEDLE MOVEMENT SENSOR
2 – FUEL INJECTOR (NUMBER 1 CYLINDER ONLY)
3 – COPPER WASHER
4 – SENSOR CONNECTOR
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FUEL SYSTEM—2.5L DIESEL ENGINE
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DESCRIPTION AND OPERATION (Continued)
2000 JEEP CHEROKEE
The flywheel has four notches at its outer edge
(Fig. 7). Each notch is spaced equally every 90°. The
notches cause a pulse to be generated when they
pass under the speed sensor (Fig. 7). These pulses
are the input to the ECM. The input from this sensor
determines crankshaft position (in degrees) by moni-
toring the notches.
The sensor also generates an rpm signal to the
ECM. This signal is used as an input for the control
of the generator field, vehicle speed control, and
instrument panel mounted tachometer.
If the engine speed sensor should fail, the system
is unable to compensate for the problem and the car
will stop.
AIR CONDITIONING (A/C) CONTROLS—ECM
INPUTS
DESCRIPTION
The A/C control system information applies to fac-
tory installed air conditioning units.
A/C REQUEST SIGNAL: When either the A/C or
Defrost mode has been selected and the A/C low and
high–pressure switches are closed, an input signal is
sent to the ECM. The ECM uses this input to cycle
the A/C compressor through the A/C relay.
If the A/C low or high–pressure switch opens, the
ECM will not receive an A/C request signal. The
PCM will then remove the ground from the A/C relay.
This will deactivate the A/C compressor clutch. Also,
if the engine coolant reaches a temperature outside
normal of its normal range, or it overheats, the ECM
will deactivate the A/C clutch.
Fig. 5 Engine Coolant Temperature Sensor Location
1 – PCM ENGINE COOLANT TEMPERATURE (ECT) SENSOR
2 – ECM ENGINE COOLANT TEMPERATURE (ECT) SENSOR
3 – ECM ECT SENSOR HARNESS CONNECTOR
4 – PCM ECT SENSOR HARNESS CONNECTOR
Fig. 6 Engine Speed Sensor Location
1 – ENGINE SPEED SENSOR
2 – GROMMET
3 – MOUNTING BOLT(S)
4 – LEFT REAR OF ENGINE
5 – TRANSMISSION
Fig. 7 Speed Sensor Operation
1 – ENGINE SPEED SENSOR
2 – FLYWHEEL
3 – NOTCHES
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FUEL SYSTEM—2.5L DIESEL ENGINE
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DESCRIPTION AND OPERATION (Continued)
2000 JEEP CHEROKEE
BRAKE SWITCH—ECM INPUT
DESCRIPTION
When the brake light switch is activated, the ECM
receives an input indicating that the brakes are
being applied. After receiving this input, the ECM is
used to control the speed control system. There is a
Primary and a Secondary brake switch. The Second-
ary brake switch is closed until the brake pedal is
pressed.
DATA LINK CONNECTOR—PCM AND ECM
INPUT AND OUTPUT
The 16–way data link connector (diagnostic scan
tool connector) links the Diagnostic Readout Box
(DRB) scan tool with the PCM and ECM. The data
link connector is located under the instrument panel
near the left body side cowl panel on left hand drive
vehicles (Fig. 8). And near the right body side cowl
panel on right hand drive vehicles (Fig. 9).
VEHICLE SPEED SENSOR—ECM INPUT
The vehicle speed sensor is located in the transfer
case extension housing (Fig. 10). The sensor input is
used by the ECM to determine vehicle speed and dis-
tance traveled.
The speed sensor generates 8 pulses per sensor
revolution. These signals, in conjunction with a
closed throttle signal from the accelerator pedal posi-
tion sensor, indicate an idle deceleration to the ECM.
When the vehicle is stopped at idle, a released pedal
signal is received by the ECM (but a speed sensor
signal is not received).
In addition to determining distance and vehicle
speed, the output from the sensor is used to control
speed control operation.
SPEED CONTROL—ECM INPUT
DESCRIPTION
The speed control system provides five separate
inputs to the ECM: On/Off, Set, Resume/Accel, Cancel,
and Decel.. The On/Off input informs the ECM that the
speed control system has been activated. The Set input
Fig. 8 Data Link Connector Location – LHD
1 – 16–WAY DATA LINK CONNECTOR
Fig. 9 Data Link Connector Location –RHD
1 – DATA LINK CONNECTOR
Fig. 10 Vehicle Speed Sensor—4 Wheel Drive
1 – 4WD TRANSFER CASE EXTENSION
2 – VEHICLE SPEED SENSOR
3 – SENSOR ELECTRICAL CONNECTOR
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FUEL SYSTEM—2.5L DIESEL ENGINE
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DESCRIPTION AND OPERATION (Continued)
2000 JEEP CHEROKEE
informs the ECM that a fixed vehicle speed has been
selected. The Resume input indicates to the ECM that
the previous fixed speed is requested.
Speed control operation will start at 50 km/h–142
km/h (35–85 mph). The upper range of operation is
not restricted by vehicle speed. Inputs that effect
speed control operation are vehicle speed sensor and
accelerator pedal position sensor.
Refer to Group 8H for further speed control infor-
mation.
ASD RELAY—ECM INPUT
DESCRIPTION
A 12 volt signal at this input indicates to the ECM
that the ASD relay has been activated. The ASD
relay is located in the PDC. The PDC is located next
to the battery in the engine compartment. For the
location of the relay within the PDC, refer to label on
PDC cover.
This input is used only to sense that the ASD relay
is energized. If the ECM does not see 12 volts (+) at
this input when the ASD relay should be activated, it
will set a Diagnostic Trouble Code (DTC).
FIVE VOLT POWER—ECM/PCM OUTPUT
DESCRIPTION
This circuit supplies approximately 5 volts to
power the Accelerator Pedal Position Sensor, and the
Boost Pressure Sensor.
ENGINE COOLANT GAUGE—PCM OUTPUT
DESCRIPTION
Refer to the Instrument Panel and Gauges group
for additional information.
ENGINE OIL PRESSURE GAUGE—PCM
OUTPUT
DESCRIPTION
Refer to the Instrument Panel and Gauges group
for additional information.
GLOW PLUG LAMP—PCM OUTPUT
DESCRIPTION
The Glow Plug lamp (malfunction indicator lamp)
illuminates on the message center each time the igni-
tion (key) switch is turned on. It will stay on for
about two seconds as a bulb test.
SPEED CONTROL—PCM OUTPUTS
DESCRIPTION
These two circuits control the fuel quantity actua-
tor to regulate vehicle speed. Refer to Group 8H for
Speed Control information.
AIR CONDITIONING RELAY—ECM OUTPUT
DESCRIPTION
This circuit controls a ground signal for operation
of the A/C clutch relay. Also refer to Air Conditioning
(A/C) Controls—ECM Input for additional informa-
tion.
The A/C relay is located in the Power Distribution
Center (PDC). The PDC is located next to the battery
in the engine compartment. For the location of the
relay within the PDC, refer to label on PDC cover.
TIMING SOLENOID—ECM OUTPUT
DESCRIPTION
The timing solenoid is located on the bottom of the
fuel injection pump (Fig. 12).
This 12(+) volt, pulse width modulated (duty–cycle)
output controls the amount of fuel timing (advance)
in the fuel injection pump. The higher the duty–cy-
cle, the lower the advance. The lower the duty–cycle,
the more advanced the fuel timing.
Fig. 11 Glow Plug Lamp Symbol
Fig. 12 Timing Solenoid
1 – FUEL INJECTION PUMP ASSEMBLY
2 – FUEL RETURN LINE
3 – FUEL SUPPLY LINE
4 – FUEL INJECTION PUMP 10–WAY CONNECTOR
5 – TIMING SOLENOID
6 – OVERFLOW VALVE
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FUEL SYSTEM—2.5L DIESEL ENGINE
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DESCRIPTION AND OPERATION (Continued)
2000 JEEP CHEROKEE
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