1993 DODGE TRUCK ignition

•

FUEL SYSTEM
14 - 59
fill
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HIAf5MflCTipQ
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The powertrain control module (PCM) has been
programmed to monitor many different circuits of the
fuel injection system. If a problem is sensed in a monitored circuit often enough to indicate an actual
problem, a diagnostic trouble code (DTC) is stored.
The DTC will be stored in the PCM memory for eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can­ cels the DTC after 51 engine starts.
Certain criteria must be met for a diagnostic trou­
ble code (DTC) to be entered into PCM memory. The criteria may be a specific range of engine rpm, en­
gine temperature and/or input voltage to the PCM.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal­
function has occurred. This may happen because one
of the DTC criteria for the circuit has not been met. Example: assume that one of the criteria for the
MAP sensor circuit is that the engine must be oper­ ating between 750 and 2000 rpm to be monitored for
a DTC. If the MAP sensor output circuit shorts to
ground when the engine rpm is above 2400 rpm, a 0
volt input will be seen by the PCM. A DTC will not
be entered into memory because the condition does not occur within the specified rpm range.
A DTC indicates that the powertrain control mod­
ule (PCM) has recognized an abnormal signal in a
circuit or the system. A DTC may indicate the result
of a failure, but never identify the failed component
directly.
There are several operating conditions that the
PCM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non-Monitored Circuits in this section.

MONITORED
CIRCUITS
The powertrain control module (PCM) can detect
certain problems in the fuel injection system.
Open or Shorted Circuit - The PCM can deter­
mine if sensor output (which is the input to PCM) is
within proper range. It also determines if the circuit is open or shorted.
Output Device Current Flow - The PCM senses
whether the output devices are hooked up.
If there is a problem with the circuit, the PCM
senses whether the circuit is open, shorted to ground
(-), or shorted to
(
+
)
voltage.
Oxygen Sensor - The PCM can determine if the
oxygen sensor is switching between rich and lean.
This is, once the system has entered Closed Loop. Re­ fer to Open Loop/Closed Loop Modes Of Operation in
the Component Description/System Operation section
for an explanation of Closed (or Open) Loop opera­ tion.
NON-MONITORED CIRCUITS

The PCM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A diagnostic trouble code (DTC) may not be displayed for these
conditions.
Fuel Pressure: Fuel pressure is controlled by the
vacuum assisted fuel pressure regulator. The PCM
cannot detect a clogged fuel pump inlet filter, clogged
in-line fuel filter, or a pinched fuel supply or return

line.
However, these could result in a rich or lean
condition causing an oxygen sensor DTC to be stored in the PCM.
Secondary Ignition Circuit: The PCM cannot de­
tect an inoperative ignition coil, fouled or worn spark

plugs,
ignition cross firing, or open circuited spark
plug cables.
Engine Timing: The PCM cannot detect an incor­
rectly indexed timing chain, camshaft sprocket or crankshaft sprocket. The PCM also cannot detect an
incorrectly indexed distributor. However, these could
result in a rich or lean condition causing an oxygen
sensor DTC to be stored in the PCM.
Cylinder Compression: The PCM cannot detect
uneven, low, or high engine cylinder compression.
Exhaust System: The PCM cannot detect
a

plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions: The PCM cannot de­
termine if the fuel injector is clogged, or the wrong injector is installed. However, these could result in a
rich or lean condition causing an oxygen sensor DTC
to be stored in the PCM.
Excessive Oil Consumption: Although the PCM
monitors exhaust stream oxygen content through ox­
ygen sensor (closed loop), it cannot determine exces­ sive oil consumption.
Throttle Body Air Flow: The PCM cannot detect
a clogged or restricted air cleaner inlet or air filter
element.
Evaporative System: The PCM will not detect a
restricted, plugged or loaded EVAP canister. Vacuum Assist: Leaks or restrictions in the vac­
uum circuits of vacuum assisted engine control sys­
tem devices are not monitored by the PCM. However, a vacuum leak at the MAP sensor will be monitored
and a diagnostic trouble code (DTC) will be gener­
ated by the PCM.
Powertrain Control Module (PCM) System
Ground: The PCM cannot determine a poor system
ground. However, a DTC may be generated as a re­
sult of this condition.
Powertrain Control Module (PCM) Connector
Engagement: The PCM cannot determine spread or
damaged connector pins. However, a DTC may be generated as a result of this condition.

14 - SO
FUEL
SYSTEM

•
HIGH
AND LOW
LIMITS

The powertrain control module (PCM) compares in­
put signal voltages from each input device. It will es­
tablish high and low limits that are programmed into it for that device. If the input voltage is not
within specifications and other diagnostic trouble code (DTC) criteria are met, a DTC will be stored in
memory. Other DTC criteria might include engine
rpm limits or input voltages from other sensors or switches. The other inputs might have to be sensed
by the PCM when it senses a high or low input volt­ age from the control system device in question.
ACCESSING DIAGNOSTIC TROUBLE CODES A stored diagnostic trouble code (DTC) can be dis­
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the malfunction indicator lamp. This lamp was formerly referred to
as the check engine lamp. The lamp is located on the
instrument panel.
They can also be displayed through the use of the
Diagnostic Readout Box II (DRB II scan tool). The
DRB II connects to the data link connector in the ve­
hicle (Fig. 37). For operation of the DRB II, refer to
the appropriate Powertrain Diagnostic Procedures service manual.
TORQUE CONVERTER
CLUTCH RELAY
A/C
CLUTCH RELAY
.
STARTER RELAY

AUTO
SHUTDOWN RELAY FUEL PUMP RELAY POWERTRAIN
DATA LINK CONTROL
CONNECTOR MODULE
J9314-164

Fig.
37
Data
Link
Connector
Location—Typical
EXAMPLES

• If the lamp flashes 4 times, pauses and flashes 1
more time, a diagnostic trouble code (DTC) number
41 is indicated.
• If the lamp flashes 4 times, pauses and flashes 6
more times, a diagnostic trouble code (DTC) number
46 is indicated. Refer to the Diagnostic Trouble Code (DTC) charts
for DTC identification. If the problem is repaired or ceases to exist, the
powertrain control module (PCM) cancels the DTC after 51 engine starts.
Diagnostic trouble codes indicate the results of a
failure, but never identify the failed component di­
rectly. The circuits of the data link connector are shown
in (Fig. 38).
J9214-20
D-1

GROUND

D-2 Im/c
D-3
SCI
TRANS

D-4
SCI
RECEIVE

D-5
IGNITION

D-6
NOT
USED

Fig.
38
Data
Link
Connector
Schematic

ERASING TROUBLE CODES The DRB II scan tool must be used to erase a di­
agnostic trouble code (DTC). Refer to the appropriate
Powertrain Diagnostic Procedures service manual for operation of the DRB II scan tool.

DRB
II
SCAN
TOOL
For operation of the DRB II scan tool, refer to the
appropriate Powertrain Diagnostic Procedures ser­
vice manual.

DIAGNOSTIC TROUBLE CODE
(DTC) On the following pages, a list of diagnostic trouble
codes is provided for all gas powered engines. A DTC indicates that the powertrain control module (PCM)
has recognized an abnormal signal in a circuit or the system. A DTC may indicate the result of a failure,
but never identify the failed component directly.

MULTI-PORT
FUEL
INJECTION
(MPI)-COMPONENT

REMOVAL/INSTALLATION
—EXCEPT DIESEL

INDEX

page

Accelerator Pedal
and Throttle
Cable
. 64

Air Conditioning (A/C) Clutch Relay
64
Air
Filter/Filter
Housing
64

Automatic Shut Down (ASD) Relay
. 64
Brake
Switch
64

Camshaft
Position
Sensor
..................
64

Charge
Air
Temperature
Sensor
64

Crankshaft Position
Sensor
64

Engine
Coolant Temperature
Sensor
65
EVAP
Canister Purge Solenoid
65

Fuel
Filter
65

Fuel Filter/Fuel Pressure Regulator—5.9L Engine
. 65

Fuel Injector(S)
67

Fuel Pressure Regulator
67

Fuel Pump Module
68

Fuel Pump Relay
68

ACCELERATOR
PEDAL
AND THROTTLE
CABLE
Refer
to
the
Accelerator Pedal
and
Throttle Cable
section
of
this group
for
removal/installation proce­

dures.

AIR
CONDITIONING (A/C) CLUTCH RELAY The A/C clutch relay
is
located
in
the
engine com­
partment (Fig.
1).

A/C CLUTCH RELAY STARTER RELAY
DATA LINK CONTROL
CONNECTOR MODULE
J9314-164

Fig.
1 Relay Location

AIR
FILTER/FILTER
HOUSING
Refer
to
Air Filter/Filter Housing—Gas Engines
in

Group
25,
Emission Control System
for
removal/in­
stallation procedures.
AUTOMATIC SHUT DOWN (ASD) RELAY The ASD relay
is
located
in
the
engine compart­
ment (Fig.
1).
page

Fuel Rail
69

Fuel System Pressure Release Procedure
......
71
Fuel Tank Pressure Relief/Rollover Valve
71

Fuel Tanks
71

Fuel
Tubes/Lines/Hoses
and
Clamps
71
Idle
Air
Control (IAC) Motor
71

Ignition Coil
71

Intake Manifold
71

Manifold Absolute Pressure (MAP)
Sensor
71

Oxygen
(02)
Sensor
72

Park/Neutral Switch
. 73

Powertrain Control Module (PCM)
73

Quick-Connect
Fittings
73

Throttle
Body
73
Throttle
Position
Sensor
(TPS)
......
74

Vehicle
Speed
Sensor
75

BRAKE
SWITCH
Refer
to
Group
5,
Brakes
for
removal/installation
procedures.

CAMSHAFT
POSITION
SENSOR
For removal/installation procedures, refer
to
Group

8D,
Ignition System. See Camshaft Position Sensor.

CHARGE
AIR
TEMPERATURE SENSOR
The intake manifold charge
air
temperature sensor
is located
in the
front/side
of
the
intake manifold (Fig.
2
or
3).

REMOVAL
(1) Remove
air
cleaner assembly.
(2) Disconnect electrical connector
at
sensor (Figs.
2
or
3). (3) Remove sensor from intake manifold.

INSTALLATION
(1) Install sensor
to
intake manifold. Tighten
to 28

Nnn (20
ft.
lbs.) torque.
(2) Install electrical connector.
(3) Install
air
cleaner.

CRANKSHAFT
POSITION
SENSOR
Refer
to
Group 8D, Ignition System
for
removal/in­
stallation procedures.

•

FUEL SYSTEM
14-71
FUEL SYSTEM PRESSURE RELEASE PROCEDURE

WARNING:
THE
FUEL
SYSTEM
IS
UNDER
A
CON­

STANT
PRESSURE
(EVEN
WITH
THE
ENGINE

TURNED
OFF).
BEFORE
SERVICING
THE
FUEL
PUMP,
FUEL
LINES
(TUBES),
FUEL
FILTER,
OR

FUEL
INJECTOR(S),
THE
FUEL
SYSTEM
PRESSURE

MUST
BE
RELEASED.

To release fuel pressure, refer to the Fuel Delivery
System section of this group. See Fuel System Pres­
sure Release Procedure.

FUEL TANKS
Refer to the Fuel Tank section of this group for re­
moval/installation procedures.

FUEL TANK
PRESSURE
RELIEF/ROLLOVER VALVE
Refer to the Fuel Tank section of this group for re­
moval/installation procedures.

FUEL
TUBES/LINES/HOSES
AND CLAMPS
Refer to Fuel Tubes/Lines/Hoses and Clamps in the
Fuel Delivery System section of this group for remov­ al/installation procedures. Also refer to Quick-Connect Fittings in the Fuel
Delivery System section of this group for removal/in­
stallation procedures.

IDLE
AIR
CONTROL
(IAC)
MOTOR
The IAC motor is located on the back of the throt­
tle body (Fig. 22).
MANIFOLD ABSOLUTE
Fig.
22
idle
Air Control Motor—Typical
REMOVAL

(1) Remove air cleaner assembly.
(2) Disconnect electrical connector from IAC motor.
(3) Remove two mounting bolts (screws) (Fig. 23).

J9214-23

Fig.
23
Mounting
Bolts
(Screws)—IAC
Motor
(4) Remove IAC motor from throttle body.

INSTALLATION
(1) Install IAC motor to throttle body.
(2) Install and tighten two mounting bolts (screws)
to 7 N»m (60 in. lbs.) torque.
(3) Install electrical connector.
(4) Install air cleaner assembly.

IGNITION COIL
Refer to Group 8D, Ignition Systems for removal/
installation procedures.

INTAKE MANIFOLD
Refer to Group 11, Exhaust System and Intake
Manifold for removal/installation procedures.

MANIFOLD ABSOLUTE
PRESSURE
(MAP)
SENSOR
The MAP sensor is located on the front of the
throttle body (Fig. 24). An L-shaped rubber fitting is
used to connect the MAP sensor to throttle body (Fig.
25).
REMOVAL
The throttle body must be removed from the intake
manifold for MAP sensor removal.
(1) Remove air cleaner assembly.
(2) Remove throttle body. Refer to Throttle Body
removal in this section.
(3) Remove two MAP sensor mounting bolts
(screws) (Fig. 24). (4) While removing MAP sensor, slide the vacuum
rubber L-shaped fitting (Fig. 25) from the throttle
body.
(5) Remove rubber L-shaped fitting from MAP sen­
sor.

DIESEL
FUEL
INJECTION—COMPONENT
DESCRIPTION/SYSTEM
OPERATION

NDEX

page

Air
Conditioning (A/C) Clutch
Relay-PCM
Output
. 81

Air
Conditioning (A/C)
Controls-PCM
Input
.... 77

Air
Intake Heater
Relays—PCM
Output
........ 81

Auto
Shut
Down
(ASD)
Relay-PCM
Output
.... 82
Automatic
Shut
Down
(ASD)
Sense-PCM
input
. 78
Battery
Voltage-PCM
Input
78

Brake
Switch—PCM
Input
....... 78

Charge
Air
Temperature
Sensor—PCM
Input
... 78
Engine
Speed
Sensor—PCM
Input
........... 78

Fuel
Drain Manifold
83

Fuel
Heater
83

Fuel
Injection
Pump
83

Fuel
Injectors
84

Fuel
Solenoid
84

Fuel/Water
Separator
Filter ................. 84

General
Information
76

Generator
Field-PCM
Output
. 81

High
Pressure
Fuel
Lines
85
Ignition
Sense—PCM
Input
78

KSB
Solenoid
....... 85

Malfunction Indicator
Lamp—PCM
Output
...... 82

Manual
Shut
Down
Lever
.................. 85

GENERAL
INFORMATION

The fuel system of the 5.9L (in-line six-cylinder)
turbo-diesel engine (Fig. 1) consists of the following components:
• Fuel tank
• Low and high pressure fuel supply lines
• Mechanical lift pump
• Fuel/water separator filter
• Fuel heater
• Fuel injection pump
• Fuel injectors • Fuel return lines For information regarding fuel requirements of the
5.9L turbo-diesel engine, refer to the Fuel Require­
ments—Diesel Engines paragraph at the front of this group. Although various components, relays and switches
are operated by the powertrain control module (PCM), the diesel fuel injection system (Fig. 1) is not
directly regulated by the PCM. Refer to the proceed­
ing Powertrain Control Module section for additional
information.

SYSTEM
DIAGNOSIS
The PCM tests many of its own input and output
circuits. If a diagnostic trouble code (DTC) is found in a major system, this information is stored in the
PCM memory. Refer to On-Board Diagnostics in the Diesel Fuel Injection—General Diagnosis section of
page

Mechanical
Lift
Pump
86

Overdrive
Indicator
Lamp—PCM
Output
....... 82

Overdrive
Solenoid-PCM
Output
............ 82

Overdrive/Override
Switch—PCM
Input
........ 79
Park/Neutral
Switch-PCM
Input
79

Power
Ground-PCM
Input
. 79
Powertrain Control Module
(PCM)
76

SCI
Receive-PCM
Input
. . 80

SCI
Transmit-PCM
Output
. . . 82

Sensor
Return-PCM
Input
................. 80

Signal
Ground-PCM
Input
. 80

Speed
Control-PCM
Input
80

Speed
Control-PCM
Output
82

System
Diagnosis
76

System
Operation
86

Tachometer-PCM
Output
82

Throttle
Position
Sensor
(TPS)-PCM
Input
80

Vehicle
Speed
Sensor-PCM
Input
80

Wait-To-Start
Lamp-PCM
Output
82

Water-ln-Fuel
Lamp-PCM
Output
83

Water-ln-Fuel
Sensor-PCM
input
80
this group for DTC information. The DRB II scan tool can be used to access the DTC messages stored in the PCM memory.

POWERTRAIN
CONTROL
MODULE
(PCM)
The powertrain control module (PCM) (Fig. 2) was
formerly referred to as the SBEC or engine control­ ler. The PCM is a pre-programmed, dual micropro­
cessor digital computer. The PCM is located in the engine compartment be­
hind the battery and under the left front fender (Fig.
2).
The PCM contains a voltage convertor, which con­
verts battery voltage to a regulated 8.0 volts. This is used to power the engine speed sensor. The PCM also
provides a 5 volt supply for the throttle position sen­sor (TPS). The TPS is not used if equipped with a
manual transmission.
Various sensors, switches and relays provide the
inputs necessary for operation of the PCM.
The PCM Inputs are from:

9
Air conditioning control switch
• Automatic shut down (ASD) sense circuit
• Battery voltage
• Brake light switch • Charge air temperature sensor ® Coolant temperature sensor (Auto, trans, only)
• Engine speed sensor
• Ignition
• Overdrive/override switch
• Park/neutral switch (Auto, trans, only)

14-78
FUEL SYSTEM

• If
the A/C low
pressure switch opens (indicating
a

low refrigerant level),
the PCM
will
not
receive
an

A/C select signal.
The PCM
will then remove
the

ground from
the A/C
relay. This will deactivate
the

A/C compressor clutch.
If evaporator switch opens, (indicating that evapo­
rator
is not in
proper temperature range),
PCM
will
not receive
the A/C
request signal.
The PCM
will
then remove
the
ground from
the A/C
relay, deacti­
vating
the A/C
compressor clutch.

AUTOMATIC SHUT DOWN
(ASD)
SENSE-PCM
INPUT
A
12
volt signal
at
this input indicates
to the PCM

that
the ASD has
been activated.
The ASD
relay
is
located
in the
engine compartment
(Fig.
3).
It is
used
to power
a
circuit
to the
generator field winding.
TORQUE
CONVERTER

CLUTCH RELAY A/C
CLUTCH RELAY
.
STARTER RELAY
AUTO
SHUTDOWN
RELAY
FUEL PUMP RELAY
DATA
LINK
CONNECTOR
POWERTRAIN
CONTROL
MODULE
J9314-164
Fig.
3
Relay Location—Typical

BATTERY VOLTAGE-PC! INPUT
The battery input provides power
to
operate
the

PCM. Battery voltage
is
needed
to
keep
PCM
mem­
ory alive.
The
memory stores diagnostic trouble code (DTC) messages
and the
minimum
TPS
value from
the previous key-on,
BRAKE
SWITCH-PCM INPUT

If
the PCM
receives
a
brake switch input while
the

speed control system
is on, it
will disable speed con­
trol.

CHARGE AIR TEMPERATURE SENSOR—PCM INPUT
The charge
air
temperature sensor
is
located
on top

of
the
intake manifold
(Fig. 4). It
provides
an
input
to
the PCM
that indicates
air
temperature
in the
manifold. Based
on the
charge
air
temperature input,
the
PCM
determines
if and how
long
to
energize
the
air intake heaters. Refer
to Air
Intake Heaters
in

this section. AIR

TEMPERATURE
SWITCH

(KSB
SOLENOID)

j9114-235

Fig.
4
Charge
Air
Temperature Sensor

ENGINE
SPEED
SENSOR-PCM
INPUT
The engine speed sensor (sometimes referred
to as

the crankshaft position sensor)
is
mounted
to the

front
of
engine
(Fig. 5). It
generates
an rpm
signal
to

the
PCM. The
engine speed sensor input
is
used along with
the
vehicle speed sensor
and
throttle
po­

sition sensor inputs
to
determine when
to
shift
the

automatic transmission into
and out of
overdrive.
The speed sensor signal
is
also used
as an
input
for
the
ASD
relay
(for
control
of
generator field), vehicle speed control
and
instrument panel mounted tachom­
eter.

SENSOR
MOUNTING BOLTS
VIBRATION
DAMPER
J9214-69

Fig.
5
Engine Speed Sensor
IGNITION
SENSE-PCM
INPUT
The ignition circuit
(J2)
sense input informs
the

PCM that
the
ignition switch
is in the run
position.

14 - 80
FUEL SYSTEM

•
SCI
RECEIVE-PCM
INPUT

The serial communication interface (SCI) receive
and transmit outputs allow the PCM to communicate
with the DRB II scan tool.

SENSOR
RETURN-PCM
INPUT
Sensor return provides a low noise ground refer­
ence for all system sensors.

SIGNAL
GROUND-PCM
INPUT
Provides a common ground for the input signals.

SPEED
CONTROL-PCM
INPUT
The PCM regulates the speed control system based
on inputs it receives. The speed control operating
range is from 35 to 85 mph. Inputs that effect speed control operation are:
• Park/neutral switch
• Vehicle speed sensor
• Throttle position sensor
• Engine speed sensor
• Brake switch

THROTTLE
POSITION SENSOR (TPS) —PCM
INPUT
The throttle position sensor is not used with man­
ual transmissions. The throttle position sensor (TPS) is mounted on
the top of the fuel injection pump (Fig. 9). The TPS
provides an input to the PCM. It senses how far the
throttle is open (past the idle position). The PCM uses the TPS input, along with vehicle speed sensor and engine speed sensor inputs to determine 3-4 up­
shift (overdrive) and 4-3 downshift. The TPS is a potentiometer. The PCM supplies 5
volts to the sensor. TPS output to the PCM varies
from approximately 1.0 volt at idle to 3.5 volts at
wide open throttle (WOT). T

J9114-237

Fig.
9
Throttle
Position
Sensor
VEHICLE SPEED SENSOR-PCM
INPUT
The vehicle speed sensor (Fig. 10) is located in the
extension housing of the transmission (2WD) or on the transfer case extension housing (4WD). A signal
is sent from this sensor, along with signals from both
the TPS and the engine speed sensor, to the PCM.
The PCM will then use this information to determine
when to shift into and out of overdrive.
The speed sensor is also used in determining speed
control set, decelerate, accelerate, maximum set
speed (85 mph) and minimum set speed (35 mph) op­
erations.
VEHICLE

SPEED

SENSOR

Fig.
10 Vehicle
Speed
Sensor—Typical Location

WATER-IN-FUEL SENSOR-PCM
INPUT
The water-in-fuel (WIF) sensor is located at the
bottom of the fuel/water separator filter (Fig. 11). The sensor sends an input to the PCM when it senses
water in the fuel. The PCM looks at the water-in-fuel sensor signal when the ignition key is put in the ON
position. It also monitors the input at the end of the intake heater post-heat cycle. The PCM turns the water-in-fuel indicator lamp to
the ON position if water is detected in the fuel. The
water-in-fuel indicator lamp is located in the instru­ ment panel.
J91 14-85

Fig.
11 Water-in-Fuel
Sensor

•

FUEL
SYSTEM
14-81
AIR
CONDITIONING
(A/C)
CLUTCH RELAY—PCM
OUTPUT
The PCM activates the A/C compressor through the
A/C clutch relay. The PCM regulates A/C compressor
operation by switching the ground circuit for the A/C
clutch relay on and off. The relay is located in the engine compartment (Fig. 3). By switching the ground path for the relay on and
off, the PCM is able to cycle the A/C compressor
clutch. This is based on changes in engine operating
conditions. If, during A/C operation, the PCM senses
a low idle speed, it will de-energize the relay. This
prevents A/C clutch engagement. The relay will re­ main de-energized until the idle speed increases.

GENERATOR
FIELD-PCM
OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. It will control
ASD relay operation. The input (through the PCM)
for the ASD relay comes from the engine speed sen­ sor. When engine running speed is above 384 rpm, a
signal is sent from the PCM to engage the ASD re­
lay. This supplies the necessary generator field wind­
ing control. When rpm drops below 320, the signal to
the ASD relay is stopped. Refer to Group 8A, for charging system information.

AIR INTAKE HEATER RELAYS-PCM
OUTPUT
The PCM operates the air intake heaters through
the air intake heater relays (Fig. 12). The relays may
be energized before and after cranking, depending upon intake manifold air temperature. The PCM
monitors intake manifold air temperature through
the charge air temperature sensor. Refer to Air In­
take Heaters in this section. The relays are not energized during engine crank­
ing. When they are energized they make a clicking
noise.

CAUTION:
Do not energize the air intake heater re­
lays
more than
once
per 15
minutes.
If the relays
are
cycled
and the key is turned off and then turned
back
on, the engine
could
be
damaged.
Wait 15

minutes
before
turning the key back to the ON po­

sition.

AIR INTAKE
HEATER
When energized, the air intake heaters warm in­
coming air as it enters the intake manifold. The air
intake heaters (Fig. 13) are energized by the PCM
through the air intake heater relays. Intake manifold air temperature determines when the heaters are en­
ergized. They may be energized before cranking and
after cranking, or both. Refer to Pre-Heat Cycle and
Post-Heat Cycle. The heaters are not energized dur­ ing cranking.
HEATER

RELAYS

WELL
J9114-67

Fig.
12 Air Intake Heater
Relays

Fig.
13 Air Intake Heaters—Typical PREHEAT CYCLE
The PCM powers up when the ignition key is
turned to the On position. If intake manifold air tem­
perature is 15°C (59°F) or below, the intake heaters are energized and the wait-to-start light is illumi­
nated. The heaters are energized for a specific amount of time. This is based on the intake manifold
air temperature. Refer to the Air Intake Heater Cy­
cle Chart.
Once the heaters have cycled, the wait-to-start
light goes out. While the engine is cranked, the heat­
ers are not energized.

POST-HEAT CYCLE
After engine has been started, the post-heat cycle
will begin if intake manifold air temperature was 15°C (59°F) or below when ignition switch was
turned on. Depending upon intake manifold temper­ ature, either: both heaters are energized, or they are
cycled on and off (when one is energized, the other is

not).
The time the heaters are energized depends upon intake manifold air temperature. Refer to the
Air Intake Heater Cycle Chart.