Jeep 1996 Grand Cherokee Service Manual page 541

8W - 30 - 2
DESCRIPTION AND OPERATION (Continued)
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 the generator field terminal, 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.
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.
VEHICLE SPEED SENSOR
Circuit K6 supplies 5 volts from the Powertrain
Control Module (PCM) to the vehicle speed sensor.
The K6 circuit connects to cavity B31 of the PCM.
8W - 30 FUEL/IGNITION SYSTEMS
Circuit G7 from the vehicle speed sensor provides
an input signal to the PCM. The G7 circuit connects
to cavity B27 of the PCM.
The PCM provides a ground for the vehicle speed
sensor signal (circuit G7) through circuit K4. Circuit
K4 connects to cavity A4 of the PCM.
HELPFUL INFORMATION
Circuit K4 splices to supply ground for the signals
from the following:
• Heated oxygen sensor
• Camshaft position sensor
• Crankshaft position sensor
• Throttle position sensor
• Manifold absolute pressure sensor
• Engine coolant temperature sensor
• Intake air temperature sensor
HEATED OXYGEN SENSORS
When the Automatic Shut Down (ASD) relay con-
tacts close, circuit A142 supplies voltage to the
upstream and downstream heated oxygen sensors.
Circuit K41 delivers the signal from the upstream
heated oxygen sensor to the Powertrain Control Mod-
ule (PCM). Circuit K41 connects to cavity A24 of the
PCM. Circuit K141 supplies the signal from the
downstream heated oxygen sensor to the PCM. Cir-
cuit K141 connects to PCM cavity A25.
The PCM provides a ground for the heated oxygen
sensor signals (circuits K41 and K141) through cir-
cuit K4. Circuit K4 connects to cavity A4 of the PCM
connector.
Circuit Z12 provides ground for the heater circuit
in each sensor.
HELPFUL INFORMATION
Circuit A142 also supplies battery voltage to the
fuel injectors, ignition coil, and generator.
Circuit K4 splices to supply ground for the signals
from the following:
• Camshaft position sensor
• Crankshaft position sensor
• Intake air temperature sensor
• Throttle position sensor
• Manifold absolute pressure sensor
• Engine coolant temperature sensor
• Vehicle speed sensor
BATTERY TEMPERATURE SENSOR
The Powertrain Control Module (PCM) determines
battery temperature on circuit T222. Circuit T222
connects the PCM to the battery temperature sensor.
Circuit T222 connects to cavity C15 of the PCM. Cir-
cuit K4 provides ground for the sensor and connects
to PCM cavity A4.
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