ECU Ram 3500 2020 Service Manual

210SAFETY
The best protection against carbon monoxide
entry into the vehicle body is a properly
maintained engine exhaust system.
Whenever a change is noticed in the sound of
the exhaust system, when exhaust fumes can
be detected inside the vehicle, or when the
underside or rear of the vehicle is damaged,
have a competent mechanic inspect the
complete exhaust system and adjacent body
areas for broken, damaged, deteriorated, or
mispositioned parts. Open seams or loose
connections could permit exhaust fumes to
seep into the passenger compartment. In
addition, inspect the exhaust system each time
the vehicle is raised for lubrication or oil
change. Replace as required.
SAFETY CHECKS YOU SHOULD MAKE
I
NSIDE THE VEHICLE
Seat Belts
Inspect the seat belt system periodically,
checking for cuts, frays, and loose parts.
Damaged parts must be replaced immediately.
Do not disassemble or modify the system.
Front seat belt assemblies must be replaced
after a collision. Rear seat belt assemblies must
be replaced after a collision if they have been
damaged (i.e., bent retractor, torn webbing,
etc.). If there is any question regarding seat belt
or retractor condition, replace the seat belt.
Air Bag Warning Light
The Air Bag warning light will turn on for four
to eight seconds as a bulb check when the
ignition switch is first turned to ON/RUN. If the
light is either not on during starting, stays on, or
turns on while driving, have the system
inspected at an authorized dealer as soon as
possible. After the bulb check, this light will
illuminate with a single chime when a fault with the Air Bag System has been detected. It will
stay on until the fault is removed. If the light
comes on intermittently or remains on while
driving, have an authorized dealer service the
vehicle immediately.
Refer to “Occupant Restraint Systems” in
“Safety” for further information.
Defroster
Check operation by selecting the defrost mode
and place the blower control on high speed. You
should be able to feel the air directed against
the windshield. See an authorized dealer for
service if your defroster is inoperable.
Floor Mat Safety Information
Always use floor mats designed to fit your
vehicle. Only use a floor mat that does not
interfere with the operation of the accelerator,
brake or clutch pedals. Only use a floor mat that
is securely attached using the floor mat
fasteners so it cannot slip out of position and
interfere with the accelerator, brake or clutch
pedals or impair safe operation of your vehicle
in other ways.
If it is necessary to sit in a parked vehicle
with the engine running, adjust your
heating or cooling controls to force outside
air into the vehicle. Set the blower at high
speed.
WARNING!
(Continued)

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SAFETY211
(Continued)
(Continued)
(Continued)
WARNING!
An improperly attached, damaged, folded, or
stacked floor mat, or damaged floor mat
fasteners may cause your floor mat to
interfere with the accelerator, brake, or clutch
pedals and cause a loss of vehicle control. To
prevent SERIOUS INJURY or DEATH:
ALWAYS securely attach your floor mat
using the floor mat fasteners. DO NOT
install your floor mat upside down or turn
your floor mat over. Lightly pull to confirm
mat is secured using the floor mat
fasteners on a regular basis.
ALWAYS REMOVE THE EXISTING FLOOR
MAT FROM THE VEHICLE before
installing any other floor mat. NEVER install
or stack an additional floor mat on top of an
existing floor mat.
ONLY install floor mats designed to fit your
vehicle. NEVER install a floor mat that
cannot be properly attached and secured to
your vehicle. If a floor mat needs to be
replaced, only use a FCA approved floor
mat for the specific make, model, and year
of your vehicle.
ONLY use the driver’s side floor mat on the
driver’s side floor area. To check for inter -
ference, with the vehicle properly parked
with the engine off, fully depress the accel -
erator, the brake, and the clutch pedal (if
present) to check for interference. If your
floor mat interferes with the operation of
any pedal, or is not secure to the floor,
remove the floor mat from the vehicle and
place the floor mat in your trunk.
WARNING! (Continued)
ONLY use the passenger’s side floor mat on
the passenger’s side floor area.
ALWAYS make sure objects cannot fall or
slide into the driver’s side floor area when
the vehicle is moving. Objects can become
trapped under accelerator, brake, or clutch
pedals and could cause a loss of vehicle
control.
NEVER place any objects under the floor
mat (e.g., towels, keys, etc.). These objects
could change the position of the floor mat
and may cause interference with the accel -
erator, brake, or clutch pedals.
If the vehicle carpet has been removed and
re-installed, always properly attach carpet
to the floor and check the floor mat
fasteners are secure to the vehicle carpet.
Fully depress each pedal to check for inter -
ference with the accelerator, brake, or
clutch pedals then re-install the floor mats.
WARNING! (Continued)
4

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212SAFETY
PERIODIC SAFETY CHECKS YOU SHOULD
M
AKE OUTSIDE THE VEHICLE
Tires
Examine tires for excessive tread wear and
uneven wear patterns. Check for stones, nails,
glass, or other objects lodged in the tread or
sidewall. Inspect the tread for cuts and cracks.
Inspect sidewalls for cuts, cracks, and bulges.
Check the wheel bolts for tightness. Check the
tires (including spare) for proper cold inflation
pressure.
Lights
Have someone observe the operation of brake
lights and exterior lights while you work the
controls. Check turn signal and high beam
indicator lights on the instrument panel.
Door Latches
Check for proper closing, latching, and locking.
Fluid Leaks
Check area under the vehicle after overnight
parking for fuel, coolant, oil, or other fluid leaks.
Also, if gasoline fumes are detected or if fuel, or
brake fluid leaks are suspected, the cause
should be located and corrected immediately.
It is recommended to only use mild soap
and water to clean your floor mats. After
cleaning, always check your floor mat has
been properly installed and is secured to
your vehicle using the floor mat fasteners
by lightly pulling mat.
WARNING! (Continued)

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226STARTING AND OPERATING
NOTE:

If ambient temperatures are low and the coolant
temperature is below 180°F (82°C), the engine
idle speed will slowly increase to 1,000 RPM after
two minutes of idle, if the following conditions are
met:

Foot is off brake pedal and throttle pedal.
Automatic transmission is in PARK.
Vehicle speed is 0 mph (0 km/h).
Applying the throttle will cancel fast idle.
Operating the exhaust brake at idle will
greatly improve warm up rate and will help
keep the engine close to operating tempera -
ture during extended idle.
ENGINE IDLING
Avoid prolonged idling, long periods of idling
may be harmful to your engine because
combustion chamber temperatures can drop so
low that the fuel may not burn completely.
Incomplete combustion allows carbon and
varnish to form on piston rings, engine valves,
and injector nozzles. Also, the unburned fuel
can enter the crankcase, diluting the oil and
causing rapid wear to the engine. If the engine is allowed to idle or the truck is
driven on low engine speed drive cycles for
more than 2 hours, the system will
automatically enter an emissions operating
mode that will increase the engine idle speed to
900 RPM. While in this mode, which is designed
to help maintain the diesel particulate filter, the
engine idle speed will return to normal when the
brake pedal is applied. A small change in engine
tone or a slight change in engine performance
while accelerating may also be noticeable at
speeds below 20 mph (32 km/h). This
operating mode may last for up to an hour of
idle time, or around 20 minutes of driving time.
Your truck may have been ordered with an
optional voltage monitoring idle up feature. If a
load is placed on the electrical system while the
truck is in park, this feature will attempt to
maintain normal system voltage by
automatically increasing engine idle speed. You
may notice several consecutive increases in
idle speed, up to a maximum of 1,450 RPM, as
the system will attempt to utilize the smallest
increase in idle speed necessary to maintain
normal system voltage. The idle speed will
return to normal when either the electrical load
is removed, or when the brake pedal is applied.
NOTE:
For instrument cluster display messages
related to the vehicle's exhaust system, refer to
“Instrument Cluster Display” in “Getting To
Know Your Instrument Panel” for further infor
-
mation.
Idle-Up Feature
The driver-controlled high idle speed feature will
help increase cylinder temperatures and
provide additional cab heat, however, excessive
idling may still cause the exhaust
aftertreatment system to not properly
regenerate. Extended periods of idle time
should be avoided.
The Idle-Up feature uses the Speed Control
switches to increase engine idle speed and
quickly warm the vehicle's interior.

1. With the transmission in PARK, the parking brake applied, and the engine running,
push the speed control switch to the ON
position, then push the SET switch.

2. The engine RPM will go up to 1,100 RPM. To increase the RPM, push and hold the
ACCEL/RESUME switch and the idle speed
will increase to approximately 1,500 RPM.
To decrease the RPM, push and hold the

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STARTING AND OPERATING229
Do Not Operate The Engine With Failed
Parts
All engine failures give some warning before the
parts fail. Be on the alert for changes in
performance, sounds, and visual evidence that
the engine requires service. Some important
clues are:
Engine misfiring or vibrating severely.
Sudden loss of power.
Unusual engine noises.
Fuel, oil or coolant leaks.
Sudden change, outside the normal oper -
ating range, in the engine operating tempera -
ture.
Excessive smoke.
Oil pressure drop.
ENGINE BLOCK HEATER — GAS ENGINE (IF
EQUIPPED)
The engine block heater warms the engine, and
permits quicker starts in cold weather. Connect
the cord to a standard 110-115 Volt AC
electrical outlet with a grounded, three-wire
extension cord.
The engine block heater cord is routed through
the grille by the right front tow hook.
It includes a removable cap that is secured by a
tethered strap. It also has a c-clip that is used
for storage when not in use for the Winter
months. During Winter months, remove the
heater cord wiring assembly from itself on the
c-clip.
The engine block heater must be plugged in at
least one hour to have an adequate warming
effect on the engine.
ENGINE BLOCK HEATER — DIESEL ENGINE
(IF EQUIPPED)
The engine block heater warms engine coolant
and permits quicker starts in cold weather.
Connect the heater cord to a ground-fault
interrupter protected 110–115 Volt AC
electrical outlet with a grounded, three-wire
extension cord.
The engine block heater cord is routed under
the hood to the right side and can be located
just behind the grille near the headlamp.
NOTE:
The engine block heater cord is a factory
installed option. If your vehicle is not equipped,
heater cords are available from an authorized
Mopar dealer.
The block heater must be plugged in at least
one hour to have an adequate warming effect
on the coolant.
CAUTION!
If oil pressure falls to less than normal
readings, shut the engine off immediately.
Failure to do so could result in immediate and
severe engine damage.
WARNING!
Remember to disconnect the engine block
heater cord before driving. Damage to the
110-115 Volt electrical cord could cause
electrocution.WARNING!
Remember to disconnect the cord before
driving. Damage to the 110–115 Volt
electrical cord could cause electrocution.
5

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234STARTING AND OPERATING
(Continued)
(Continued)
NOTE:
You must press and hold the brake pedal while
shifting out of PARK.
IGNITION PARK INTERLOCK
This vehicle is equipped with an Ignition Park
Interlock which requires the transmission to be
in PARK before the ignition can be turned to the
OFF mode. This helps the driver avoid
inadvertently leaving the vehicle without placing
the transmission in PARK. This system also
locks the transmission in PARK whenever the
ignition is in the OFF mode.
NOTE:
The transmission is NOT locked in PARK when
the ignition is in the ACC mode (even though the
engine will be off). Ensure that the transmission
is in PARK, and the ignition is OFF (not in ACC
mode) before exiting the vehicle.
It is dangerous to shift out of PARK or
NEUTRAL if the engine speed is higher than
idle speed. If your foot is not firmly pressing
the brake pedal, the vehicle could accel -
erate quickly forward or in reverse. You
could lose control of the vehicle and hit
someone or something. Only shift into gear
when the engine is idling normally and your
foot is firmly pressing the brake pedal.
Unintended movement of a vehicle could
injure those in or near the vehicle. As with
all vehicles, you should never exit a vehicle
while the engine is running. Before exiting a
vehicle, always come to a complete stop,
then apply the parking brake, shift the
transmission into PARK, and turn the igni -
tion OFF. When the ignition is in the OFF
mode, the transmission is locked in PARK,
securing the vehicle against unwanted
movement.
When exiting the vehicle, always make sure
the ignition is in the OFF mode, remove the
key fob from the vehicle, and lock the
vehicle.
WARNING! (Continued)
Never leave children alone in a vehicle, or
with access to an unlocked vehicle.
Allowing children to be in a vehicle unat -
tended is dangerous for a number of
reasons. A child or others could be seriously
or fatally injured. Children should be
warned not to touch the parking brake,
brake pedal or the transmission gear
selector.
Do not leave the key fob in or near the
vehicle (or in a location accessible to chil -
dren), and do not leave the ignition in the
ACC or ON/RUN mode. A child could
operate power windows, other controls, or
move the vehicle.
CAUTION!
Damage to the transmission may occur if the
following precautions are not observed:
Shift into or out of PARK or REVERSE only
after the vehicle has come to a complete
stop.
WARNING! (Continued)
Do not shift between PARK, REVERSE,
NEUTRAL, or DRIVE when the engine is
above idle speed.
Before shifting into any gear, make sure
your foot is firmly pressing the brake pedal.
CAUTION! (Continued)

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236STARTING AND OPERATING
(Continued)
(Continued)
PARK (P)
This range supplements the parking brake by
locking the transmission. The engine can be
started in this range. Never attempt to use
PARK while the vehicle is in motion. Apply the
parking brake when exiting the vehicle in this
range.
When parking on a level surface, you may shift
the transmission into PARK first, and then apply
the parking brake.
When parking on a hill, apply the parking brake
before shifting the transmission to PARK. As an
added precaution, turn the front wheels toward
the curb on a downhill grade and away from the
curb on an uphill grade.
NOTE:
On four-wheel drive vehicles be sure that the
transfer case is in a drive position.
When exiting the vehicle, always:
Apply the parking brake.
Shift the transmission into PARK.
Turn the engine off.
Remove the key fob.
WARNING!
Never use the PARK position as a substi
-
tute for the parking brake. Always apply the
parking brake fully when exiting the vehicle
to guard against vehicle movement and
possible injury or damage.
Your vehicle could move and injure you and
others if it is not in PARK. Check by trying to
move the transmission gear selector out of
PARK with the brake pedal released. Make
sure the transmission is in PARK before
exiting the vehicle.
The transmission may not engage PARK if
the vehicle is moving. Always bring the
vehicle to a complete stop before shifting to
PARK, and verify that the transmission gear
position indicator solidly indicates PARK (P)
without blinking. Ensure that the vehicle is
completely stopped, and the PARK position
is properly indicated, before exiting the
vehicle.
It is dangerous to shift out of PARK or
NEUTRAL if the engine speed is higher than
idle speed. If your foot is not firmly pressing
the brake pedal, the vehicle could accel -
erate quickly forward or in reverse. You
could lose control of the vehicle and hit
someone or something. Only shift into gear
when the engine is idling normally and your
foot is firmly pressing the brake pedal.

Unintended movement of a vehicle could
injure those in or near the vehicle. As with all
vehicles, you should never exit a vehicle
while the engine is running. Before exiting a
vehicle, always come to a complete stop,
then apply the parking brake, shift the trans -
mission into PARK, and turn the ignition OFF.
When the ignition is in the OFF mode, the
transmission is locked in PARK, securing the
vehicle against unwanted movement.
When exiting the vehicle, always make sure
the ignition is in the OFF mode, remove the
key fob from the vehicle, and lock the
vehicle.

WARNING! (Continued)

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STARTING AND OPERATING241
(Continued)
(Continued)
The following indicators should be used to
ensure that you have properly engaged the
transmission into the PARK position:
When shifting into PARK, pull the gear
selector toward you and move it all the way
counterclockwise until it stops.
Release the gear selector and make sure it is
fully seated in the PARK gate.
Look at the transmission gear position
display and verify that it indicates the PARK
position (P).
With brake pedal released, verify that the
gear selector will not move out of PARK.
REVERSE (R)
This range is for moving the vehicle backward.
Shift into REVERSE only after the vehicle has
come to a complete stop.
It is dangerous to shift out of PARK or
NEUTRAL if the engine speed is higher than
idle speed. If your foot is not firmly pressing
the brake pedal, the vehicle could accel -
erate quickly forward or in reverse. You
could lose control of the vehicle and hit
someone or something. Only shift into gear
when the engine is idling normally and your
foot is firmly pressing the brake pedal.
Unintended movement of a vehicle could
injure those in or near the vehicle. As with
all vehicles, you should never exit a vehicle
while the engine is running. Before exiting a
vehicle, always come to a complete stop,
then apply the parking brake, shift the
transmission into PARK, turn the engine off,
and remove the key fob. When the ignition
is in the LOCK/OFF (key removal) position
(or, with Keyless Enter-N-Go, when the igni -
tion is in the OFF mode), the transmission is
locked in PARK, securing the vehicle
against unwanted movement.
When leaving the vehicle, always make
sure the ignition is in the OFF mode,
remove the key fob from the vehicle, and
lock the vehicle.
WARNING! (Continued)
Never leave children alone in a vehicle, or
with access to an unlocked vehicle.
Allowing children to be in a vehicle unat -
tended is dangerous for a number of
reasons. A child or others could be seriously
or fatally injured. Children should be
warned not to touch the parking brake,
brake pedal or the transmission gear
selector.
Do not leave the key fob in or near the
vehicle (or in a location accessible to chil -
dren), and do not leave the ignition (in a
vehicle equipped with Keyless Enter-N-Go)
in the ACC or ON/RUN mode. A child could
operate power windows, other controls, or
move the vehicle.
CAUTION!
Before moving the transmission gear
selector out of PARK, you must turn the igni -
tion to the ON/RUN mode, and also press
the brake pedal. Otherwise, damage to the
gear selector could result.
WARNING! (Continued)
DO NOT race the engine when shifting from
PARK or NEUTRAL into another gear range,
as this can damage the drivetrain.
CAUTION! (Continued)
5

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STARTING AND OPERATING259
The locking axles are controlled by the axle lock
buttons.
Under normal driving conditions, the vehicle
should be left in the AXLE UNLOCK position.
NOTE:
Even when the axles are in the AXLE UNLOCK
position, the limited slip differential in the rear
axle still provides torque biasing capability for
moderate low traction environments.
During the command to lock the axle, the
indicator light will flash until the axle is locked.
After the lock command has been successfully
executed, the light will remain on solid. To lock the rear axle, place the vehicle in 4WD
LOW, 4WD HIGH or 2WD. Refer to “Four Wheel
Drive Operation” in “Starting And Operating” for
further information. Push the REAR LOCK
button while traveling less than 10 mph
(16 km/h). The REAR LOCK indicator light will
remain on when the rear axle is locked.
NOTE:
Left to right wheel speed difference may be
necessary to allow the axle to fully lock. If the
indicator light is flashing after placing the
vehicle in the REAR LOCK or FRONT/REAR LOCK
position, drive the vehicle in a turn or on loose
gravel to expedite the locking action.
To lock the front axle, push the FRONT/REAR
LOCK button while traveling less than 10 mph
(16 km/h) in 4WD LOW. The FRONT/REAR
LOCK indicator light will be solid when the front
axle is locked.
NOTE:
The rear axle must be locked before the front
axle will lock.
When both the axles are locked, to unlock the
front axle, push the REAR LOCK button while in
4WD LOW. The FRONT/REAR LOCK indicator
light will go out when the axle is unlocked.
NOTE:
The axle lockers could be torque locked due to
side to side loads on the axle. Driving slowly
while turning the steering wheel from a left
hand turn to a right hand turn or driving in
REVERSE for a short distance may be required
to release the torque lock and unlock the axles.
To unlock the rear axle, push the AXLE UNLOCK
button. The REAR LOCK indicator light will go
out when the rear axle is unlocked.
Do not try to lock the rear axle if the vehicle
is stuck and the tires are spinning. You can
damage drivetrain components. Lock the
rear axle before attempting situations or
navigating terrain, which could possibly
cause the vehicle to become stuck.
CAUTION!
(Continued)
WARNING!
Do not use the locked axle position for normal
driving. A locked front axle is intended for
off-road driving only. Locking the front axle
during on-road driving will reduce the steering
ability. This could cause a collision and you
may be seriously injured.
5

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262STARTING AND OPERATING
The Basics Of Off-Road Driving
You will encounter many types of terrain driving
off-road. You should be familiar with the terrain
and area before proceeding. There are many
types of surface conditions: hard packed dirt,
gravel, rocks, grass, sand, mud, snow and ice.
Every surface has a different effect on your
vehicle's steering, handling and traction.
Controlling your vehicle is one of the keys to
successful off-road driving, so always keep a
firm grip on the steering wheel and maintain a
good driving posture. Avoid sudden
accelerations, turns or braking. In most cases
there are no road signs, posted speed limits or
signal lights. Therefore you will need to use your
own good judgment on what is safe and what
isn't. When on a trail you should always be
looking ahead for surface obstacles and
changes in terrain. The key is to plan your future
driving route while remembering what you are
currently driving over.
When To Use Low Range
When driving off-road, shift into 4WD LOW for
additional traction or to improve handling and
control on slippery or difficult terrain. Due to the
lower gearing, low range will allow the engine to
operate in a higher power range. This will allow
you to idle over obstacles and down hills, with
improved control and less effort. Also, use 4WD
LOW in rain, ice, snow, mud, and sand to get
heavy loads rolling, improve traction, or
whenever 4WD HIGH traction will not do the job.
DRIVING IN SNOW, MUD AND SAND
There is a drastic reduction in traction when
driving in snow, mud or sand. The vehicle will be
less responsive to steering, acceleration and
braking inputs. Therefore you should accelerate
slowly, leave greater stopping distances and
avoid abrupt vehicle maneuvers. You want to
keep a slow constant steady pace. The key is to
maintain the vehicle's momentum.
Snow – In heavy snow or for additional
control and traction at slower speeds, shift
the transmission to a low gear and shift the
transfer case to 4WD LOW if necessary. Do
not shift to a lower gear than necessary to
maintain headway. Over-revving the engine
can spin the wheels and traction will be lost.
If you start to slow to a stop, try turning your
steering wheel no more than a quarter turn
quickly back and forth, while still applying
throttle. This will allow the tires to get a fresh
"bite" and help maintain your momentum.
Mud – Deep mud creates a great deal of
suction around the tires and is very difficult to
get through. You should use 4WD LOW with a
gear low enough to maintain your momentum
without shifting. If you start to slow to a stop,
try turning your steering wheel no more than
a quarter turn quickly back and forth for addi -
tional traction. Mud holes pose an increased
threat of vehicle damage and getting stuck.
WARNING!
Always wear your seat belt and firmly tie down
cargo. Unsecured cargo can become
projectiles in an off-road situation.
CAUTION!
Never park your vehicle over dry grass or
other combustible materials. The heat from
your vehicle exhaust system could cause a
fire.
CAUTION!
On icy or slippery roads, do not downshift at
high engine RPMs or vehicle speeds because
engine braking may cause skidding and loss
of control.

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