Jeep 1997 Grand Cherokee Service Manual page 1242

8W - 30 - 34
DESCRIPTION AND OPERATION (Continued)
PCM GROUND (DIESEL)
Ground for the Powertrain Control Module (PCM)
is supplied on the Z12 circuit. This circuit connects to
four cavities in the PCM and terminates at the PCM
ground location.
DATA LINK CONNECTOR
Circuit A250 from fuse 11 in the Power Distribu-
tion Center (PDC) powers circuit F75 through fuse 7
in the junction block. Circuit F75 supplies battery
voltage to the data link connector.
Circuit D84 connects to cavity C29 of the PCM.
Circuit D84 is the SCI transmit circuit for the Pow-
ertrain Control Module (PCM). Circuit D83 connects
to cavity C27 of the PCM and cavity A3 of the Con-
troller- Anti Lock Brakes. Circuit D83 is the SCI
receive circuit for the PCM.
Circuits D83 and D98 from the speed proportional
steering module connect to the data link connector.
Circuits Z1 and Z2 provide ground for the data link
connector.
AUTOMATIC SHUT DOWN (ASD) RELAY
When the ignition switch is in either the START or
RUN position, it connects circuit A1 from fuse 8 in
the Power Distribution Center (PDC) to circuit A21.
Circuit A21 powers circuit F99 through PDC fuse 18.
Circuit F99 feeds the coil side of the Automatic Shut
Down (ASD) relay. The Powertrain Control Module
(PCM) provides ground for the relay on circuit K900.
Circuit K900 connects to cavity C3 of the PCM.
When the PCM grounds the ASD relay, contacts
inside the relay close and connect circuit F5 from
fuse 20 in the PDC to circuit A142. Circuit A142
splices to, fuel injectors, ignition coil and the
upstream and downstream heated oxygen sensors.
Circuit A142 also connects to cavity C12 of the PCM.
HELPFUL INFORMATION
Along with supplying voltage to the coil side of the
ASD relay, circuit F99 also supplies voltage to the
coil side of the fuel pump relay.
AUTOMATIC SHUT DOWN RELAY (DIESEL)
Power for the coil and contact side of the Auto-
matic Shut Down (ASD) relay is supplied on circuit
F5. This circuit is HOT at all times and protected by
a 25 amp fuse located in the Power Distribution Cen-
ter (PDC).
Ground for the coil side of the relay is controlled by
the Powertrain Control Module (PCM) on circuit
K900.
When the PCM provides a ground for the coil side
of the relay the contacts in the relay CLOSE and
connect circuits F5 and A142. The A142 circuit sup-
8W - 30 FUEL/IGNITION SYSTEMS
plies power to various components and modules in
the fuel system.
HELPFUL INFORMATION
• Check the 25 amp fuse located in the PDC
• Refer to the appropriate section of the service
manual or Diagnostic Test Procedures manual
FUEL PUMP RELAY
When the ignition switch is in either the START or
RUN positions, it connects circuit A1 from fuse 8 in
the Power Distribution Center (PDC) to circuit A21.
Circuit A21 powers circuit F99 through PDC fuse 18.
Circuit F99 supplies battery voltage to the coil side of
the fuel pump relay. The Powertrain Control Module
(PCM) provides ground for the relay on circuit K81.
Circuit K81 connects to cavity C19 of the PCM.
When the PCM grounds the fuel pump relay, con-
tacts inside the relay close and connect circuit A61
from fuse 16 in the PDC to circuit A64. Circuit A64
feeds the fuel pump motor (part of the in-tank fuel
pump module).
HELPFUL INFORMATION
Circuit F99 also powers the coil side of the Auto-
matic Shut Down (ASD) relay.
FUEL PUMP MODULE
The in-tank fuel pump module contains the fuel
pump motor and fuel level sensor.
FUEL PUMP MOTOR
When the fuel pump relay contacts close, the relay
feeds the fuel pump motor. Circuit A64 from the
relay powers the fuel pump module. Circuit Z1 pro-
vides ground for the fuel pump motor.
FUEL LEVEL SENSOR
The fuel level sensor is a variable resistor. Circuit
G40 provides the fuel level input to cavity C26 of the
Powertrain Control Module (PCM). The PCM broad-
casts fuel level data on the CCD bus. The micro-pro-
cessor in the instrument cluster receives the message
on the CCD bus, calculates fuel gauge needle position
and adjusts the gauge.
FUEL PUMP MODULE (DIESEL)
The in-tank fuel pump module contains the fuel
pump motor and fuel level sensor.
FUEL PUMP MOTOR
When the fuel pump relay contacts close, the relay
feeds the fuel pump motor. Circuit A64 from the
relay powers the fuel pump motor. Circuit Z1 pro-
vides ground for the fuel pump motor.
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