DODGE TRUCK 1993 Service Repair Manual

2i
- 4
EMISSION
CONTROL
SYSTEMS

•
VACUUM
HOSE
ROUTING
SCHEMATICS

The following vacuum hose routing schematics
are used
as
examples only.
If
there
are any
differ­
ences between these schematics
and the
Vehicle
Emission Control Information (VECI) label schemat­

ics,
those shown
on the
VECI label should
be
used.
ENGINE
VACUUM
SCHEMATIC-3.9U5.2L/5.9L
LDC
ENGINES

TO ATMOSPHERE
i
TRANSDUCER

FUEL
TANK

PRESSURE
RELIEF
ROLLOVER VALVE

W/ORIFICE

EVAP
CANISTER
TO CLIMATE CONTROL,
CRUISE
CONTROL,
4WD
AXLE

(WHEN
EQUIPPED) INTAKE
MANIFOLD
ORIFICE ENGINE
VALVE
COVER FUEL PRESSURE
REGULATOR
M

P
= MANIFOLD VACUUM
= PORTED VACUUM

"8^
EGR
VALVE
EVAP PURGE SOLENOID MAP

SENSOR

CHECK VALVE W/ORIFICE
CRANKCASE

BREATHER
TO
AIR
CLEANER
ENGINE VALVE
COVER TO BRAKE
BOOSTER FRONT
OF
VEHICLE
J9325-13

EMISSION
CONTROL
SYSTEMS
25 • I

ENGINE
VACUUM SCHEMATIC-5,9L HOC ENGINE
M =
MANIFOLD VACUUM
P
=
PORTED VACUUM EVAP

CANISTER
ROLLOVER VALVE

W/ORIFICE

CRANKCASE
BREATHER
DOWNSTREAM
AIR

t t
TO CLIAAATE CONTROL,
VEHICLE
SPEED
CONTROL, 4X4 AXLE

(WHEN
EQUIPPED)
TO BRAKE
BOOSTER
AIR PUMP INTAKE MANIFOLD
ORIFICE
CHECK
VALVE
W/ORIFICE
J9325-34

25
- 6
EMISSION CONTROL
SYSTEMS

•
EWAPORATIWE EMISSION CONTROLS

INDEX

page

Crankcase
Breather/Filter—Gas Powered
Engines
. . . 9

EVAP
(Evaporation)
Control
System
. 6

EVAP
Canister
. . 6
page

Evap
Canister
Purge
Solenoid
6

Fuel Tank
Filler
Tube
Cap . 7

Positive
Crankcase
Ventilation
(PCV)
System
.... 7

Pressure
Relief/Rollover Valve
6

EVAP (EVAPORATION) CONTROL SYSTEM GENERAL
INFORMATION
The function
of the
EVAP control system
is to
pre­
vent
the
emissions
of
gasoline vapors from
the
fuel
tank into
the
atmosphere. When fuel evaporates
in
the fuel tank,
the
vapors pass through vent hoses
or

tubes
to a
carbon filled EVAP canister. They
are

temporarily held
in the
canister until they
can be

drawn into
the
intake manifold when
the
engine
is

running.
The vapors
are
drawn into
the
engine
at
idle
as

well
as off
idle. This system
is
called
a
Bi-level Purge
System where there
is a
dual source
of
vacuum
to re­

move fuel vapor from
the
EVAP canister. The EVAP canister
is a
feature
on all
models
for

the storage
of
fuel vapors from
the
fuel tank.
The hoses used
in
this system
are
specially
manufactured.
If
replacement becomes neces­ sary,
it is
important
to use
only fuel resistant
hose.

PRESSURE
RELIEF/ROLLOVER VALVE
These vehicles
are
equipped with
a
combination
pressure relief
and
rollover valve. This dual function valve will relieve fuel tank pressure
and
also prevent
fuel flow through
the
fuel tank vent hoses
in the
event
of an
accidental vehicle rollover. The valve incorporates
a
pressure relief mechanism
that releases fuel tank pressure when
the
pressure increases above
the
calibrated sealing value. Refer
to

the Fuel Tank section
of
Group
14,
Fuel Systems
for

removal
and
installation procedures.

EVAP CANISTER
A sealed, maintenance free, EVAP canister
is
used
on
all
vehicles.
The
canister
is
mounted
in the en­
gine compartment
on the
right side wheel well
(Fig.
1).
The
EVAP canister
is
filled with granules
of an

activated carbon mixture. Fuel vapors entering
the

EVAP canister
are
absorbed
by the
charcoal gran­
ules.
Fuel tank pressure vents into
the
EVAP canister.
Fuel vapors
are
temporarily held
in the
canister
un­

til they
can be
drawn into
the
intake manifold.
The
EVAP canister purge solenoid allows
the
EVAP can­ ister
to be
purged
at
predetermined times
and at
cer­
tain engine operating conditions.
Refer
to the
Component Removal/Installation sec­
tion
of
this group
for
replacement procedures.

EVAPORATIVE
Fig.
1
EVAP
Canister Location

EVAP CANISTER PURGE SOLENOID
Vacuum
for the
EVAP canister
is
controlled
by the

EVAP canister purge solenoid
(Fig. 2). The
solenoid
is operated
by the
powertrain control module (PCM).
The
PCM
regulates
the
solenoid
by
switching
the

ground circuit
on and off
based
on
engine operating conditions. When energized,
the
solenoid prevents
vacuum from reaching
the
EVAP canister. When
not
energized,
the
solenoid allows vacuum
to
flow
through
to the
EVAP canister. During warm-up
and for a
specified time period
af­

ter
hot
starts,
the PCM
grounds
the
EVAP canister purge solenoid causing
it to
energize. This will pre­
vent vacuum from reaching
the
EVAP canister
valve. When
the
engine reaches
an
operating temper­ ature
of
approximately 27°C (80°F)
and a
time delay
interval
of
about
100
seconds
has
occurred,
the PCM

removes
the
ground
to
solenoid.
The
de-energized
so­
lenoid allows vacuum
to
flow
to the
EVAP canister and purge fuel vapors through
the
intake manifold. The EVAP canister purge solenoid will also
be en­

ergized during certain idle conditions
in
order
to up­

date
the
fuel delivery calibration. Refer
to the
Component Removal/Installation sec­
tion
of
this group
for
replacement procedures.

•

Fig.
2
EVAP
Canister
Purge
Solenoid—Typical

FUEL
TANK
FILLER
TUBE
CAP
The fuel tank is sealed with a pressure-vacuum re­
lief fuel tank filler tube cap (Fig. 3). The relief valves
in the cap are a safety feature. They operate only to
prevent excessive pressure or vacuum in tank caused
by a malfunction in system or damage to vent lines.

PLASTIC
GASKET

RN348

Fig.
3
Fuel
Tank
Filler
Tube Cap—Typical
The cap has a threaded configuration. This allows
the seal to be broken and pressure to be relieved without separation of cap from filler tube. Approxi­
mately two and a half turns are required to remove
the cap.
If replacement of filler tube cap is necessary, it
must be replaced with an identical cap to be sure of
correct system operation.

CAUTION:
Remove
the
fuel
tank
filler
tube cap to

relieve
any
fuel
tank
pressure.
The cap
must
be re­

moved
prior to
disconnecting
any
fuel
system
com­

ponent or before draining the
fuel
tank, •—-
EMISSION
CONTROL
SYSTEMS
25 - 7

Fig.
4 PCV Valve/Hose—Typical
A closed engine crankcase breather/filter, with a
hose connecting it to the air filter housing, provides
the source of air for system.
The PCV system operates by engine intake mani­
fold vacuum (Fig. 5). Filtered air is routed into the
crankcase through the air filter hose and crankcase
breather/filter. This forces crankcase vapors through
the PCV valve. It is then drawn into a passage in the intake manifold. Here it becomes part of the cali­
brated air/fuel mixture to be consumed in the com­ bustion chamber. The PCV system constantly ventilates the crankcase to help prevent sludge for­
mation and vapors from entering the atmosphere.
POSITIVE CRANKCASE VENTILATION (PCV) VALVE The PCV valve contains a spring loaded plunger.
This plunger meters the amount of crankcase vapors
routed into the combustion chamber based on intake
manifold vacuum.
When the engine is not operating or during an en­
gine popback, the spring forces the plunger back
against the seat. This will prevent vapors from flow­
ing through the valve (Fig. 6).
During periods of high manifold vacuum, such as
idle or cruising speeds, vacuum is sufficient to com­
pletely compress spring. It will then pull the plunger
to the top of the valve (Fig. 7). In this position there is minimal vapor flow through the valve.
POSITIVE
CRANKCASE
VENTILATION
(PCV)

SYSTEM

DESCRIPTION/OPERA
TION
All gas engines are equipped with a closed crank­
case ventilation system and PCV valve (Fig. 4).
This system consists of a crankcase PCV valve
mounted on the cylinder head (valve) cover with a
hose extending from the valve to the intake mani­ fold.

25 - 8
EMISSION
CONTROL
SYSTEMS

•

Fig.
5 Typical
Closed
Crankcase
Ventilation
System
J9025-20

Fig.
6
Engine
Off or
Engine
PopBack—No
Vapor
Flow

J8925-14

Fig.
7
High
Intake Manifold Vacuum—Minimal Vapor
Flow

During periods of moderate manifold vacuum, the
plunger is only pulled part way back from inlet. This
results in maximum vapor flow through the valve
(Fig. 8).
J8925-15

Fig.
8 Moderate Intake Manifold Vacuum—Maximum Vapor Flow TESTING
(1) With engine idling, remove the PCV valve from
cylinder head (valve) cover. If the valve is not
plugged, a hissing noise will be heard as air passes through the valve. Also, a strong vacuum should be
felt at the valve inlet (Fig. 9).

Fig.
9
Check
Vacuum
at PCV Valve—Typical
(2) Install the PCV valve. Remove the crankcase
breather/filter. Hold a piece of stiff paper, such as a
parts tag, loosely over the opening of crankcase
breather/filter at the cylinder head (valve) cover (Fig.
10).

(3) The paper should be drawn against the opening
in the cylinder head (valve) cover with noticeable
force. This will be after allowing approximately one minute for crankcase pressure to reduce.
CRANKCASE
BREATHER
—
REMOVED
J9325-17

Fig.
10
Check
Vacuum
at
Crankcase
Breather
Opening—Typical

•

EMISSION
CONTROL
SYSTEMS
25 - 9 (4) Turn engine off and remove PCV valve from
cylinder head (valve) cover. The valve should rattle
when shaken (Fig. 11).
Fig. 11
Shake
PCV Valve-Typical
Replace the PCV valve and retest the system if it
does not operate as described in the preceding tests.
Do not attempt to clean the old PCV valve.
(5) If the paper is not held against the opening in
cylinder head (valve) cover after new valve is in­ stalled, the PCV valve hose may be restricted and
must be replaced. The passage in the intake manifold
must also be checked and cleaned. To clean the intake manifold fitting, turn a 1/4
inch drill (by hand) through the fitting to dislodge
any solid particles. Blow out the fitting with shop air. If necessary, use a smaller drill to avoid remov­
ing any metal from the fitting.
CRANKCASE
BREATHER/FILTER-GAS POWERED

ENGINES
The crankcase breather/filter (Fig. 12) is located on
the cylinder head (valve) cover. It must be kept clean and lubricated. At the recommended interval, remove
the filter and wash it thoroughly in kerosene or sim­ ilar solvent. Lubricate or wet the filter by inverting
it and filling with SAE 30 engine oil. Filter must
then be thoroughly drained. More frequent service
may be necessary for vehicles operated extensively on short run, stop and go or extended engine idle ser­

vice.
The filter must be replaced at correct intervals. Re­
fer to Lubrication and Maintenance, Group 0 in this service manual. 8925-28
Fig. 12 Crankcase Breather/Filter—Gas Powered
Engines

25-10
EMISSION
CONTROL
SYSTEMS

EXHAUST
EMISSION
CONTROLS

INDEX

page

Air Inlet—5.9L Diesel
Engine
13
Exhaust
Gas Recirculation (EGR)
Systems
10

HEATED
INLET
AIR
SYSTEM

The air filter housing mounted-heated inlet air sys­
tem is no longer used on any Dodge Truck gas pow­ ered engine.

EXHAUST
GAS
RECIRCULATION
(EGR)
SYSTEMS
GENERAL INFORMATION The EGR system reduces oxides of nitrogen (NOx)
in the engine exhaust and helps prevent spark
knock. This is accomplished by allowing a predeter­
mined amount of hot exhaust gas to recirculate and
dilute the incoming fuel/air mixture. This dilution
reduces peak flame temperature during combustion.
The system consists of an intake manifold mounted
EGR valve (Fig. 1) and connecting hoses. The vac­
uum to the EGR is controlled by the electric EGR
transducer (EET) (Figs. 1 and 2). The EET is a dual
electric/vacuum function switch. It is controlled by
engine vacuum and the powertrain control module (PCM).
Fig. 1 EGR System—Gas Powered Engines
EGR OPERATION The electric exhaust gas recirculation transducer
(EET) is a back pressure transducer and an electric
vacuum solenoid combined into a single unit (Figs. 1 and 2). The vacuum solenoid portion of the EET re­
ceives its electrical signal from the powertrain con­
trol module (PCM). Using this signal, the solenoid regulates the vacuum flowing through to the trans­ ducer portion of the EET. The back pressure trans-
page

Heated
Inlet
Air
System
. 10

Oxygen
(02)
Sensor
13

ELECTRICAL
VACUUM

CONNECTION
SUPPLY
9125-34

Fig.
2 Electric EGR Transducer
(EET)—Gas

Powered
Engines
ducer measures the amount of exhaust gas back
pressure on the exhaust side of the EGR valve. It
then varies the strength of the vacuum signal ap­
plied to the EGR valve. The transducer uses this
back pressure signal to provide the correct amount of exhaust gas recirculation under all conditions.
The vacuum supply for the EGR valve is controlled
by the EET. The electrical solenoid portion of the EET is controlled by the powertrain control module (PCM). The PCM monitors engine coolant tempera­
ture and other operating conditions to determine
when EGR operation is desired. Refer to Open Loop/ Closed Loop Modes of Operation in Group 14, Fuel
Systems for a description of EGR solenoid operation
based on engine operating conditions.
If the electrical connector to the EET is dis­
connected or the electrical signal is lost, the
EGR valve will operate at all times. This results
in poor engine performance and reduced driveability
during certain operating conditions.
Vacuum flows between the solenoid portion of the
EET and the transducer portion of the EET. This
happens only when the solenoid is not electrically en­ ergized. The transducer is connected to the EGR
valve by a vacuum hose and a back pressure hose.
The transducer is controlled by exhaust back pres­ sure and is ported to the exhaust manifold through a
hose connecting it to the bottom of the EGR valve.
Vacuum will be supplied to the EGR valve and
EGR operation will begin when:

•

EMISSION
CONTROL
SYSTEMS
25 - 11 • The electrical solenoid portion of the EET is not
energized.
• The engine back pressure entering the EGR valve
inlet is strong enough to close the transducer bleed
valve.
If back pressure is not strong enough to close the
transducer bleed valve, the transducer will bleed off the vacuum preventing EGR operation.
When the electrical solenoid portion of the EET is
de-energized by the powertrain control module (PCM), vacuum flows to the transducer. The trans­
ducer is connected to the engine exhaust system by a small hose that connects to the base of the EGR
valve.
The vacuum section of the transducer is controlled
by exhaust system back pressure. When back pres­ sure is high enough it will close a bleed valve in the
transducer allowing vacuum to actuate the EGR
valve. If back pressure does not close the bleed valve,
vacuum will be bled off.
For more information, refer to Group 14, Fuel Sys­

tems.
Refer to the Component Removal/Installation sec­
tion of this group for EGR valve replacement proce­
dures.

EGR SYSTEM ON-BOARD DIAGNOSTICS
(CALIFORNIA VEHICLES
ONLY)

The powertrain control module (PCM) performs an
On-Board Diagnostic (OBD) check of the EGR system
on all California vehicles. The diagnostic system uses
the electric EGR transducer (EET) for the system

tests.

The OBD check activates only during selected en­
gine/driving conditions. When the conditions are met,
the PCM energizes the EET solenoid to disable the EGR. The PCM checks for a change in the oxygen sensor signal. If the air-fuel mixture goes lean, the
PCM will attempt to enrichen the mixture. The PCM
registers a diagnostic trouble code (DTC) if the EGR system has failed or degraded. After registering a

DTC,
the PCM turns the malfunction indicator
lamp (MIL) on. (The malfunction indicator lamp was formerly referred to as the check engine lamp). The
malfunction indicator lamp indicates the need for im­
mediate service.
If a malfunction is indicated by the malfunction in­
dicator lamp and a DTC for the EGR system was set,
check for proper operation of EGR system. Use the
following: System Test, EGR Gas Flow Test and EGR
Diagnosis Chart.
If the EGR system tests properly, check the system
using the DRB II scan tool. For use of the DRB II,
refer to the appropriate Powertrain Diagnostics Pro­ cedure service manual. EGR SYSTEM SERVICE
A malfunctioning EGR system can cause engine
spark knock, sags or hesitation, rough idle, engine
stalling and poor driveability. To be sure of proper
operation of the EGR system, inspect all passages for
blockage. Check moving parts for binding. Inspect
the complete system for leaks. Replace system com­ ponents or hoses that are leaking.
Inspect all hose connections between throttle body,
intake manifold, EGR valve and EGR purge solenoid.
Replace any vacuum harness components that are
leaking or damaged. Refer to EGR Control System Test and EGR Gas
Flow Test to check EGR System operation.
EGR GAS FLOW TEST (1) Disconnect hose from EGR valve and connect a
hand vacuum pump to EGR valve nipple. Apply a
minimum of 12 inches vacuum the valve.
(2) The engine should now idle roughly or stall. If
this occurs, the valve is performing correctly. Proceed
to Electric EGR Transducer Test.
(3) If the engine idle speed did not change, remove
the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage. Repair as nec­
essary. If blockage is not present, replace the EGR
valve.
ELECTRIC EGR TRANSDUCER (EET)

TESTING ELECTRIC SOLENOID PORTION OF TRANSDUCER
(1) Bring the engine to normal operating tempera­

ture.
Operate at idle speed. Test the EET as follows: (2) Check vacuum at EET vacuum source. Discon­
nect the hose and attach a vacuum gauge to it.
(3) Vacuum should be a minimum of 15 inches:
• If vacuum is low, check the line for kinks, twists
or a loose connection at vacuum connector or intake
manifold.
• If vacuum is correct, remove gauge. Connect the
vacuum line and proceed to next step. (4) Check EET operation using the appropriate
Powertrain Diagnostic Procedures service manual.
Refer to this manual for use of the DRB II scan tool and repair EET as necessary.

TESTING VACUUM PORTION
OF
TRANSDUCER
(1) Disconnect the EET vacuum lines, back pres­
sure line and electrical connector. Remove trans­
ducer.
(2) Plug the EET EGR valve port.
(3) Apply 1-2 pounds air pressure to exhaust back
pressure port. Air pressure can be supplied with a
hand operated air pump or compressed air (regulated
to correct psi).
(4) Apply a minimum of 12 inches of vacuum to
vacuum supply port.
Replace the EET if it will not hold vacuum.

25
- 12
EMISSION
CONTROL
SYSTEMS
EGR
DIAGNOSIS
CHART

NOTE: ALL TESTS MUST BE MADE
WITH
FULLY
WARM ENGINE RUNNING CONTINUOUSLY FOR
AT
LEAST TWO MINUTES
WARNING: BE SURE
TO
APPLY PARKING BRAKE AND/OR BLOCK WHEELS BEFORE PERFORMING IDLE CHECK
OR
ADJUSTMENT,
OR ANY
ENGINE RUNNING TESTS
OR
ADJUSTMENTS.

Condition
Possible Cause
Correction

EGR
VALVE STEM

DOES
NOT MOVE
ON

SYSTEM
TEST.
(a) Cracked, leaking, disconnected or
plugged hoses.

EGR
VALVE STEM

DOES
NOT MOVE
ON

SYSTEM
TEST.

OPERATES
NORMALLY
ON EXTERNAL

VACUUM
SOURCE.
ENGINE
WILL
NOT

IDLE.
DIES OUT
ON

RETURN
TO
IDLE
OR

IDLE
IS
VERY ROUGH
OR SLOW.
(a) Defective control system—Plugged passages.
(b) Defective control system—solenoid or solenoid control circuit,
(a) High EGR valve leakage in closed
position.
(b) EGR tube to intake manifold leak.
(c) Solenoid or control signal to solenoid failure. (a)
(b)
(a)
(b)
(a) Verify correct hose connections and leak
check and confirm that alt hoses are open.
If defective hoses are found, replace hose
harness.
Disconnect hose harness from EGR vacuum
transducer and connect auxiliary vacuum supply. Raise engine rpm to 2000 rpm and hold. Apply 10" Hg vacuum while checking
valve movement. If no valve movement oc­
curs,
replace valve/transducer assy. If valve
opens (approx. 3mm or 1/8" travel), hold
supply vacuum to check for diaphragm
leakage. Valve should remain open 30
seconds or longer. If leakage occurs, replace
valve/transducer assy. If valve is satisfac­
tory, check control system. Remove throttle body and inspect port (slot
type) in throttle bore and associated passage in throttle body. Use suitable sol­
vent to remove deposits and check for flow
with light air pressure. Normal operation
should be restored to EGR system. Refer to Group 14. General Diagnosis "On
Board Diagnostics" to check solenoid.
If removal of vacuum hose from EGR valve
does not correct rough idle,
(a
1)
Turn
engine off. Remove the air cleaner ex­ posing the inlet to the throttle body.
(a2) Disconnect the backpressure hose from the EGR valve.
(a3) Using a nozzle with a rubber grommet con­ nection, direct compressed air (50 to 60 psi)
down through the steel backpressure tube on
the EGR valve while opening and closing the
throttle blade.
(a4) If the sound from the compressed air changes distinctly in step a3, the poppet is leaking
and air is entering the intake manifold. Replace the EGR valve.
Remove tube and visually inspect tube seal
on gasket. Tube end should be uniformally
indented on gasket with no signs of leak. If
signs of exhaust gas leakage are present, replace gaskets and tighten flange nuts to
23 N-m (200 in. lbs.). If an intake plenum
leak persists, replace EGR tube and gaskets,
following installation instructions.
Verify correct hose connections and leak
check and confirm that all hoses are open. If defective hoses are found, replace nose
harness.
(cl) Refer to Group 14, General Diagnosis "On Board Diagnostics" to check solenoid. (b)
(c)
NOTE:
DO
NOT
ATTEMPT
TO CLEAN BACK-PRESSURE EGR VALVE, REPLACE
ENTIRE VALVE/TRANSDUCER ASSEMBLY
IF
NECESSARY.

9225-26

EMISSION
CONTROL
SYSTEMS
25 - 13

For electrical tests
of the EET and its
circuitry,
re­

fer
to the
appropriate Powertrain Diagnostic Proce­ dures service manual
for use of the DRB II
scan tool.
Refer
to the
Component Removal/Installation sec­
tion
of
this group
for EET
replacement procedures.

OXYGEN
(02)
SENSOR
For description, operation, diagnosis
and
removal/
installation procedures
of the 02
sensor, refer
to
Group
14,
Fuel Systems.

AIR
INLET—5.9L
DIESEL
ENGINE
The diesel engine
air
inlet system consists
of the:

•
Air
filter housing
• Filter element •
Air
filter housing-to-turbocharger inlet tube
•
Air
crossover tube •
Air
intake heaters Ambient
air
enters
the air
filter housing through
an opening
at the
bottom
of the
housing
(Fig. 3). Air

in
the
housing
is
filtered
by the air
filter element (Fig.
4)
before
it is
drawn into
the
turbocharger.
Fig.
4 Air Filter
Element—Diesel The turbocharger increases
the
amount
of air
flow
to
the
engine.
The
turbocharger allows
the
engine
to
use
a
higher air-to-fuel ratio. This results
in im­

proved emissions.
Air flows from
the
turbocharger into
the
inter-
cooler
(Fig. 5). Air
leaves
the
intercooler, passes
through
the air
intake heaters
and
enters
the
intake manifold.

TURBOCHARGER
TURBOCHARGER
TO INTERCOOLER

INTERCOOLER
J9114-238
Fig.
5
Intercooler—Diesel
AIR INTAKE HEATER-DIESEL ENGINE The
air
intake heater warms
the
intake
air
before
it enters
the
manifold.
If
intake manifold
air
temper­ ature
is
below
16°C
(60°F)
the
powertrain control
module
(PCM)
will energize
the
heaters through
the
air intake heater relays
for
start-up
and
initial
warm-up. Refer
to
Group
14,
Fuel Systems
for
addi­
tional information. The heater
is
located
on top of the
intake manifold,
below
the air
crossover tube
(Fig. 6).

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
then turned
off,
wait
15
minutes
before turning
the key to the
ON
position.
The
15
minute period
is to
prevent damaging
the
engine.

AIR INTAKE HEATER RELAYS-DIESEL ENGINE The powertrain control module
(PCM)
operates
the

air intake heaters through
the air
intake heater
re­

lays
(Fig. 7). The
relays
are
energized before crank­
ing
if the
charge
air
temperature sensor input
to the

PCM indicates
air
temperature
is 16°C
(60°F)
or be-