Dodge RAM TRUCK 1500 1995 Service Manual page 580

SW - 3 0 - 8
8W-30 FUEL/IGNITION—DIESEL ENGINES
B R
sor changes, the resistor changes the current flow
through second coil in the fuel gauge. A change in
current flow alters the magnetic field in the fuel
gauge, which changes the pointer position.
FUEL HEATER RELAY
When the ignition switch is in the START or RUN
position, it connects circuit Al from fuse 3 in the
PDC to circuit A21. Circuit A21 powers circuit F18
through fuse 9 in the fuse block. Circuit F18 supplies
battery voltage to the coil side of the fuel heater re­
lay. , Circuit Z12 provides ground for the coil side of
the relay.
Circuit A12 from the Power Distribution Center
(PDC) supplies battery voltage to the contact side of
the fuel heater relay. When voltage is present on cir­
cuit F18, the relay energizes and its contacts close to
connect circuits A12 and A93.
Circuit A93 supplies power to the fuel heater. Cir­
cuit Z12 provides ground for the fuel heater.
FUEL'SHUT DOWN RELAY
When the engine starter motor relay energizes, its
contacts close and connect circuit A2 from fuse 2 in
the Power Distribution Center (PDC) to circuit T40.
Circuit T40 supplies battery voltage to the engine
starter motor solenoid and to the coil side of the fuel
shut down relay.
Circuit Z12 provides ground for the coil side of the
relay.
Circuit A18 from the Power Distribution Center
(PDC) supplies battery voltage to the contact side of
the fuel heater relay. When voltage is present on cir­
cuit T40, the relay energizes and its contacts close to
connect circuits A18 and A123. Circuit A123 supplies
power to one of the two coils in the fuel shut down
solenoid.
When circuit A123 energizes, the fuel shut down
solenoid raises the injection pump shut down lever to
the RUN position.
When the ignition switch is released to the RUN
position, it connects circuit Al from fuse 3 in the
PDC to circuit A21. Circuit A21 powers circuit F18
through fuse 9 in the fuse block. Circuit F18 supplies
battery voltage to the second coil in the fuel shut
down lever. When Circuit F18 energizes, the fuel
shut down solenoid holds the injection pump shut
down lever in the RUN position.
Circuit Z12 provides ground for the fuel shut down
solenoid. Refer to Group 14, Fuel Systems, for fuel
shut down solenoid operation.
INTAKE MANIFOLD AIR HEATER RELAYS
When the ignition switch is in the START or RUN
position, it connects circuit Al from fuse 3 in the
PDC to circuit A21. Circuit A21 powers circuit F18
through fuse 9 in the fuse block. Circuit F18 supplies
battery voltage to the coil side of each intake mani­
fold air heater relay.
The Powertrain Control Module (PCM) provides
ground for the coil in each relay on separate circuits.
The PCM grounds first relay on circuit S21; it
grounds the second relay on circuit S22.
When the first intake manifold air heater relay en­
ergizes, its contacts close and connect circuit A19
from the left battery positive terminal to circuit A58.
Circuit A58 connects to the intake air heater.
When the second intake manifold air heater relay
energizes, its contacts close and connect circuit A8
from the left battery positive terminal to circuit
A122. Circuit A122 connects to the intake air heater.
The intake manifold air heaters are case grounded.
Refer to Group 14, Fuel Systems, for intake manifold
heater Pre-Heat and Post-Heat Cycles.
MALFUNCTION INDICATOR LAMP (MIL)
The PCM provides ground for the instrument clus­
ter malfunction indicator lamp on circuit G3. Circuit
G3 connects to cavity 32 of the PCM. Circuit F14
provides voltage for the lamp. The MIL displays the
message CHECK ENGINE when illuminated.
For information regarding diagnostic trouble code
access using the MIL lamp, refer to Group 14, Fuel
Systems.
TACHOMETER
The tachometer module in the instrument cluster
operates the tachometer. The Powertrain Control
Module (PCM) supplies the signal for the tachometer
on circuit G21. Circuit G21 connects to cavity 43 of
the PCM.
THROTTLE POSITION SENSOR
From the Powertrain Control Module (PCM), cir­
cuit K6 supplies 5 volts to the Throttle Position Sen­
sor (TPS). Circuit K6 connects to cavity 6 of the
PCM.
Circuit K22 delivers the TPS signal to the PCM.
Circuit K22 connects to cavity 22 of the PCM.
The PCM provides a ground for the throttle posi­
tion sensor signal (circuit K22) through circuit K4.
Circuit K4 connects to cavity 4 of the PCM.
Refer to Group 14 for throttle position sensor oper­
ation.
HELPFUL INFORMATION
Circuit K4 splices to supply ground for signals from
the following:
• intake air temperature sensor
@ vehicle speed sensor
• engine speed sensor
© water-in-fuel sensor