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JX
DESCRIPTION AND OPERATION (Continued)
the PCM will be displayed. Refer to On-Board Diag-
nostics in Group 25, Emission Control Systems Diag-
nostic Trouble Code Descriptions.
RADIATOR FAN RELAYS—PCM OUTPUT
The PCM energizes the radiator fans through
either the low or high speed radiator fan relay. The
PCM controls the ground circuit for the solenoid side
of the relay. Power for both relay solenoids is sup-
plied through a 10 amp fuse in the PDC. Power for
both relay contacts is supplied power through a 40
amp fuse in the PDC. Refer to Group 8W - Wiring
Diagrams for circuit information.
The PCM monitors the A/C compressor discharge
(high side) pressure through the air conditioning
pressure transducer. Depending on engine coolant
temperature and A/C system high side pressure, both
fans operate at either low or high speed.
The radiator fan relays are located in the PDC.
The inside top of the PDC cover has a label showing
relay and fuse location.
SPEED CONTROL RELAY—PCM OUTPUT
When the operator engages the speed control PCM
receives a input from the speed control On switch. In
response to the input, the PCM grounds the coil side
of the speed control relay. The ignition switch supplies
power to the coil and contact sides of the relay. When
energized, the speed control relay supplies battery
voltage to the speed control vacuum and vent servos.
Refer to Group 8H for speed control information.
SPEED CONTROL SERVOS—PCM OUTPUT
The PCM operates the speed control vacuum and vent
servos. The PCM supplies a ground for both servos. The
speed control relay supplies, also operated by the PCM,
supplies battery voltage to the servos. When the PCM
supplies a ground to the vacuum servo, the speed con-
trol system opens the throttle plate to obtain or main-
tain the selected road speed. When the PCM supplies a
ground to the vent servo, the speed control system
releases the throttle plate. The PCM balances the two
servos to maintain the set speed. Refer to Group 8H for
speed control information.
TACHOMETER—PCM OUTPUT
The tachometer receives its information across the
CCD Bus from the Body Control Module (BCM).
Information on engine RPM is transmitted from the
Powertrain Control Module (PCM) across the CCD
Bus to the BCM. The BCM calculates the position of
the tachometer pointer based on the input from the
PCM and adjusts the position of the gauge pointer to
the necessary position. This signal is sent over the
CCD Bus to the instrument cluster.
5 VOLT SUPPLY—PCM OUTPUT
The PCM supplies 5 volts to the following sensors:
• A/C pressure transducer
• Engine coolant temperature sensor
• Manifold absolute pressure sensor
• Throttle position sensor
8-VOLT SUPPLY—PCM OUTPUT
The PCM supplies 8 volts to the crankshaft posi-
tion sensor, camshaft position sensor.
THROTTLE BODY
The throttle body mounts to the intake manifold. The
throttle position sensor and idle air control motor attach
to the throttle body (Fig. 31) or (Fig. 32).
At above idle conditions, air flow through the
throttle body is controlled by a cable operated throt-
tle blade. During closed throttle idle conditions, the
idle air control motor controls air flow. Refer to Idle
Air Control Motor in this section.
Fig. 31 Throttle Body—2.4L Engines
FUEL SYSTEM
14 - 39
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