Jeep 1997 Grand Cherokee Service Manual page 1247

ZG
DESCRIPTION AND OPERATION (Continued)
FUEL QUANTITY ACTUATOR
Power for the fuel quantity Actuator is supplied on
circuit A142. This circuit is HOT when the contacts
in the diesel Powertrain Control Module (PCM) relay
are CLOSED. Ground for the Actuator is controlled
by the PCM on circuit K140.
FUEL HEATER (DIESEL)
When the ignition switch is in the START or RUN
position, it connects circuit A1 from fuse 8 in the
Power Distribution Center (PDC) to circuit A21. Cir-
cuit A21 powers circuit F99 through PDC fuse 18.
Circuit F99 feeds the coil side of the fuel heater
relay. Ground for the relay is supplied by circuit Z4.
When the contacts of the fuel heater relay are
closed they connect circuit A12 from fuse 4 of the
PDC and circuit A64. Circuit A64 supplies voltage to
the fuel heater. Ground for the fuel heater is sup-
plied on circuit Z1.
INSTRUMENTED FIRST INJECTOR (DIESEL)
The instrumented first injector is used to provide a
input to the Powertrain Control Module (PCM). Cir-
cuit K67 connects from the PCM connector, cavity 12,
to the injector and is used as the signal wire.
Circuit K68, from cavity 11 of the PCM connector,
is used for a return from the injector.
GLOW PLUGS (DIESEL)
The glow plugs used on this vehicle are controlled
by the Powertrain Control Module (PCM) and the
glow plug relay. Power for the coil side of the relay is
supplied on circuit A142. This circuit is HOT when
the contacts in the diesel Powertrain Control Module
(PCM) relay are CLOSED.
The ground side of the relay is controlled by the
PCM on circuit K152. This circuit connects to cavity
50 of the PCM connector.
When the PCM determines a need for glow plug
operation it supplies a ground path on circuit K152.
This causes the contacts in the relay to CLOSE con-
necting circuit A0 and K154. The A0 circuit is HOT
at all times. Circuit K154 connects from the relay to
the glow plugs.
The glow plugs are case grounded.
IGNITION COIL
When the Automatic Shut Down (ASD) relay contacts
close, circuit A142 supplies voltage to the ignition coil.
The Powertrain Control Module (PCM) controls the
ground path for the ignition coil on circuit K19. Circuit
K19 connects to cavity A7 of the PCM.
HELPFUL INFORMATION
Circuit A142 splices to supply voltage to the fuel
injectors, PCM, heated oxygen sensors, and genera-
tor.
8W - 30 FUEL/IGNITION SYSTEMS
IDLE AIR CONTROL (IAC) MOTOR
The Powertrain Control Module (PCM) operates
the idle air control motor through 4 circuits; K39,
K40, K59, and K60. Each circuit connects to separate
cavities in the PCM connector.
• Circuit K39 connects to cavity A20 of the PCM
• Circuit K40 connects to cavity A11 of the PCM
• Circuit K59 connects to cavity A10 of the PCM
• Circuit K60 connects to cavity A19 of the PCM
DUTY CYCLE EVAP\PURGE SOLENOID
When the ignition switch is in 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
powers to the Duty Cycle EVAP/Purge solenoid.
The Powertrain Control Module (PCM) provides
the ground path for the solenoid on circuit K52. Cir-
cuit K52 connects to cavity C20 of the PCM.
EGR SOLENOID (DIESEL)
Power for the EGR solenoid is supplied on circuit
A142. This circuit is HOT when the contacts in the
diesel Powertrain Control Module (PCM) relay are
CLOSED. Ground for the solenoid is supplied on cir-
cuit Z1.
The PCM controls the operation of the solenoid by
supplying a ground path for circuit K35. This circuit
connects to cavity 25 of the PCM connector
LOW COOLANT LEVEL SWITCH (DIESEL)
When the low coolant level switch closes, it con-
nects circuit G18 from the Powertrain Control Mod-
ule (PCM) and circuit K167. Circuit K167 connects to
circuit K4 sensor ground circuit.
When the low coolant level switch is closed the
PCM receives a signal from circuit G18.
CCD BUS
Circuits D1 and D2 connect the Powertrain Control
Module (PCM) to the CCD Bus. Circuit D1 connects
to cavity C30 of the PCM. Circuit D2 connects to cav-
ity C28 of the PCM. Circuits D1 and D2 are a
twisted pair of wires.
Several modules and controllers broadcast and
receive data on the CCD Bus. Each module or con-
troller is enabled to receive only certain messages.
The PCM broadcasts the following messages on the
CCD bus.
• Engine RPM
• Injector on-time and distance pulses
• Vehicle speed
• Engine temperature
• Battery temperature
• Oil pressure
8W - 30 - 39