relay DODGE RAM 1999 Service Repair Manual

WAIT-TO-START Warning Light
WAIT-TO-START warning light is located on instrument panel,
just below the speedometer. WAIT-TO-START warning light will come on
for a short period and then go off as a bulb and wiring circuit test
each time ignition switch is turned to the ON position. If Engine
Control Module (ECM) determines intake manifold air temperature is
less than 59
F (15C) by input signal received from intake manifold
air temperature sensor, ECM delivers output signal to operate WAIT-TO-
START warning light and intake manifold air heater for a preheat
cycle.
WAIT-TO-START warning light will remain on until intake
manifold air heater preheat cycle is complete. WAIT-TO-START warning
light will flash on and off if intake manifold air temperature sensor
signal to ECM is not within a specified value and Diagnostic Trouble
Code (FTC) will be stored in ECM memory.
WATER-IN-FUEL Warning Light
WATER-IN-FUEL warning light is located on instrument panel,
just below tachometer. WATER-IN-FUEL warning light will come on for a
short period and then go off as a bulb and wiring circuit test each
time ignition switch is turned to the ON position. If Engine Control
Module (ECM) determines water exists in fuel/water separator by input
signal from Water-In-Fuel (WIF) sensor, ECM will deliver output signal\
to turn on the WATER-IN-FUEL warning light.
ECM/PCM OUTPUT SIGNALS
A/C Clutch Relay
The Engine Control Module (ECM) controls A/C compressor
operation by controlling ground circuit for A/C clutch relay. ECM de-
energizes A/C clutch relay if engine coolant temperature is more than
257
F (125C). The A/C clutch relay is located in power distribution
center at driver's side front corner of engine compartment, near the
battery.
Automatic Shutdown (ASD) Relay
The Engine Control Module (ECM) controls ASD operation by
controlling ground circuit for ASD relay. ASD provides voltage to
operate generator field control for charging system. ASD relay is
located in power distribution center at driver's side front corner of
engine compartment, near the battery. Automatic Shutdown (ASD) relay
may also be referred to as Auto Shutdown (ASD) relay.
CCD Bus
These circuits are connected between Engine Control Module
(ECM) and Powertrain Control Module (PCM) to allow communication
between modules.
Cruise Control System
Engine Control Module (ECM) regulates cruise control system
operation by controlling vacuum at cruise control servo. Vacuum is
controlled by use of vacuum and vent solenoids in cruise control
servo.
Data Link Connector
Engine Control Module (ECM) provides output information at
Data Link Connector (DLC) when using scan tool to perform various
tests on the ECM and electronic control system. Data link connector is
a 16-pin connector located at lower edge of driver's side of
instrument panel, just above the accelerator pedal.
5-Volt Sensor Supply Output
Powertrain Control Module (PCM) supplies a 5-volt reference

signal to the transmission solenoid assembly for transmission
temperature sensor.
Generator Field
Engine Control Module (ECM) provides output signals to
generator field for regulating charging system voltage at 12.9-15.0
volts. ECM contains an internal electronic voltage regulator for
controlling the charging system voltage.
Generator Light
If Engine Control Module (ECM) senses a low charging system
condition, generator light on instrument panel (if equipped) will be
turned on. Generator light may also come on momentarily at low idle
speed when all accessories are on.
Malfunction Indicator Light (MIL)
The MIL is located on the instrument panel, just below
tachometer and may also be referred to as the CHECK ENGINE light. MIL
comes on for a short period and then goes off as a bulb and wiring
circuit test each time ignition switch is turned to the ON position.
If Engine Control Module (ECM) receives an incorrect signal or
receives no signal from certain sensors or components, ECM will turn
on the MIL to warn the driver that a malfunction exists in the
electronic system.
Overdrive Indicator Light (A/T Models)
Engine Control Module (ECM) delivers output signal to operate\
transmission overdrive indicator (O/D OFF) light in accordance with
position of the transmission overdrive switch. If overdrive is turned
off with transmission overdrive switch, transmission overdrive
indicator light will be turned on. Transmission overdrive indicator
light is located on instrument panel, just below the speedometer.
Tachometer
Engine Control Module (ECM) delivers output signal to operate\
tachometer on instrument panel to indicate engine RPM.
Transmission Overdrive Solenoid (A/T Models)
Engine Control Module (ECM) delivers output signal to
transmission overdrive solenoid for controlling transmission overdrive
shifts. Transmission overdrive solenoid is located on transmission
valve body.
Transmission Relay (A/T Models)
Transmission relay may be referred to as transmission control
relay or transmission 12-volt supply relay. Transmission relay ground
circuit is controlled by the Engine Control Module (ECM). When ground
circuit is completed, transmission relay supplies voltage to solenoid
assembly on the transmission. Transmission relay is located in power
distribution center at driver's side front corner of engine
compartment, near the battery.
Transmission Temperature Warning Light (A/T Models With
Heavy-Duty Transmission)
Engine Control Module (ECM) delivers output signal to turn on\
transmission temperature warning light if transmission fluid
temperature is determined to be greater than 280
F (138C) by the
transmission temperature sensor. Transmission temperature warning
light is located on instrument panel, just below the tachometer.
Transmission Torque Converter Clutch Solenoid (A/T Models)
Engine Control Module (ECM) delivers an output signal to
operate transmission torque converter clutch solenoid for torque

Module (FPCM). Because of electronic control, pump timing is not
adjustable. See ON-VEHICLE ADJUSTMENTS - TRUCKS - DIESEL article.
FUEL FILTER/WATER SEPARATOR
Fuel filter/water separator is located on left side of engine
and contains fuel heater, Water-In-Fuel (WIF) sensor and drain valve.
See Fig. 2 . The WIF sensor delivers an input signal to Engine Control
Module (ECM) when water exists in fuel filter/water separator. ECM
will then turn on WATER-IN-FUEL warning light. WATER-IN-FUEL warning
light is located on instrument panel, just below tachometer. The
WATER-IN-FUEL warning light informs the operator to drain water from
fuel filter/water separator to prevent damage to fuel system
components. Water may be drained from fuel filter/water separator by
using drain valve on fuel filter/water separator.
FUEL HEATER
Fuel heater is used to prevent diesel fuel from waxing during
cold temperatures. Fuel heater is located in fuel filter/water
separator. See Fig. 2. Fuel flows from fuel tank to fuel transfer pump
and then to fuel filter/water separator. Fuel heater contains a fuel
heater temperature sensor that senses the fuel temperature. When
temperature is less than 37-53
F (3-12C), fuel heater temperature
sensor allows current to flow to the fuel heater to warm the fuel.
When temperature is more than 67-83
F (19-28C), fuel heater
temperature sensor turns off the current flow to the fuel heater.
Voltage to operate fuel heater is provided from ignition switch,
through fuel heater relay and to fuel heater. Fuel heater and fuel
heater relay are not controlled by Engine Control Module (ECM).
EMISSION SYSTEMS
INTAKE MANIFOLD AIR HEATER SYSTEM
Intake manifold air heater is used to warm intake air during
cold starting conditions. Heater system consists of 2 relays and 2
grid heaters installed on top of intake manifold. See Fig. 5.
Engine Control Module (ECM) energizes intake manifold air
heater relays to provide voltage to intake manifold air heater before
and after starting depending on input signals from intake manifold air
temperature sensor, engine speed sensor and vehicle speed. Intake
manifold air heater relays are not energized when intake manifold air
temperature is greater than 59
F (15C) or during engine cranking.
Intake manifold air heater relays are mounted on left inner wheelwell,
below left side battery. See Fig. 6.
Intake manifold air temperature sensor monitors intake
manifold air temperature and delivers an input signal to ECM for
controlling intake manifold air heater. Intake manifold air
temperature sensor is located in intake manifold. See Figs. 2 and 4.
SELF-DIAGNOSTIC SYSTEM
DATA LINK CONNECTOR
The Data Link Connector (DLC) is a 16-pin connector located
at lower edge of driver's side of instrument panel, just above the
accelerator pedal. The Engine Control Module (ECM) contains a self-
diagnostic system which stores a Diagnostic Trouble Code (FTC) if an
incorrect signal or no signal is received from certain sensors or
components. FTC may be retrieved from ECM for system diagnosis by


E - T H EO RY/O PER ATIO N - R W D - G ASO LIN E

1999 D odge P ic ku p R 1500
1999 ENGINE PERFORMANCE
CHRY - Theory & Operation - Trucks & RWD Vans - Gasoline
Dakota, Durango, Ram Pickup, Ram Van, Ram Wagon
INTRODUCTION
This article covers the basic description and operation of
engine performance related systems and components. Read this article
before working on unfamiliar systems.
COMPUTERIZED ENGINE CONTROLS
POWERTRAIN CONTROL MODULE (PCM)
The PCM is a digital computer that controls ignition timing,
air/fuel ratio, fuel injector pulse width, ignition coil(s), spark
advance, emission control devices, cooling fan, charging system, idle
speed, cruise control (if equipped), fuel pump and tachometer. For PCM\
location, see PCM LOCATION. PCM uses data from various input sources
to control output devices in order to achieve optimum engine
performance for all operating conditions.
PCM has voltage converters that convert battery voltage to
regulated 5-volt output. The 5-volt output powers battery temperature
sensor, Camshaft Position (CMP) sensor on models equipped with
Distributorless Ignition System (DIS) or distributor on models without\
DIS, Crankshaft Position (CKP) sensor, Engine Coolant Temperature
(ECT) sensor, Intake Air Temperature (IAT) sensor, logic circuits,
Manifold Absolute Pressure (MAP) sensor, Throttle Position (TP) sens\
or
and Vehicle Speed Sensor (VSS) on some models.
PCM LOCATION









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Application Location
Dakota & Durango ................. Right Front Fender, Near Firewall
Ram Pickup, Ram Van & Ram Wagon .... On Firewall, Near Wiper Motor









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NOTE: Components are grouped into 2 categories. The first category,
INPUT DEVICES, includes components that control or produce
voltage signals monitored by the PCM. The second category,
OUTPUT SIGNALS, includes components controlled by the PCM
(this is accomplished by the PCM grounding individual
circuits).
INPUT DEVICES
Vehicles are equipped with different combinations of input
devices. Not all devices are used on all models. To determine
component location and input usage on a specific model, see
appropriate wiring diagram in WIRING DIAGRAMS article. Available input
signals include:
A/C Switch
Switch signals PCM that A/C has been selected. PCM then
activates A/C compressor clutch relay and maintains idle speed at a
preprogrammed RPM. This is done through control of Idle Air Control

drive plate. PCM uses this information to determine fuel injection
sequence, ignition signal and spark timing.
Cruise Control Switch
Cruise control switch provides PCM with 3 separate inputs.
ON/OFF switch input informs PCM that cruise control system has been
activated. SET/COAST switch input informs PCM that set vehicle speed
has been selected, or if depressed will decelerate until switch is
released. RESUME/ACCEL switch input informs PCM that a previously set
speed has been selected or, if depressed, will increase speed until
released. PCM uses these inputs to control cruise control servo.
Engine Coolant Temperature (ECT) Sensor
ECT sensor monitors engine coolant temperature. PCM uses ECT
sensor information to adjust air/fuel mixture and idle speed and to
control radiator cooling fans as necessary.
Fuel Level Sensor
PCM supplies a 5-volt reference signal to fuel module in gas
tank. Fuel level sensor sends a signal to PCM indicating fuel level.
PCM monitors this signal to prevent a false misfire signal if fuel
level is less than 15 percent. PCM also sends this signal to fuel
gauge.
Heated Oxygen Sensor (HO2S)
HO2S produces a small electrical voltage (0-1 volt) when
exposed to heated exhaust gas. HO2S is electrically heated for faster
warm-up. Heating element is powered through Auto Shutdown (ASD) relay.\
HO2S acts like a rich/lean (air/fuel ratio) switch by
monitoring oxygen content in exhaust gas. This information is used by
PCM to adjust air/fuel ratio by adjusting injector pulse width.
HO2S produces low voltage when oxygen content in exhaust gas
is high. When oxygen content in exhaust gas is low, HO2S produces a
higher voltage.
Ignition Switch
Ignition switch sends signal to PCM indicating whether switch
is on, off or cranking (ST). When PCM receives ON signal, it energizes\
ASD relay coil and supplies power to sensors and actuators. When PCM
receives ST signal, it controls fuel injection rate, idle speed,
ignition timing, etc. for optimum cranking conditions.
Intake Air Temperature (IAT) Sensor
IAT sensor measures temperature of incoming intake air. This
information is used by PCM to adjust air/fuel mixture.
Manifold Absolute Pressure (MAP) Sensor
MAP sensor monitors intake manifold vacuum. Sensor transmits
information on manifold vacuum and barometric pressure to PCM. MAP
sensor information is used with information from other sensors to
adjust air/fuel mixture.
Oil Pressure Sensor
Sensor sends a signal to PCM to indicate oil pressure.
Park/Neutral (P/N) Switch (A/T Models)
This switch may also be referred to as a Park/Neutral
Position (PNP) switch. P/N switch is available on vehicles equipped
with A/T only. Switch prevents engine starter from engaging if vehicle
is in any gear except Park or Neutral.
P/N switch input (varied with gear selection) is used to
determine idle speed, fuel injector pulse and ignition timing.

diagram in appropriate WIRING DIAGRAMS article. For theory
and operation on each output component, refer to indicated
system.
A/C Clutch Relay
See A/C CLUTCH RELAY under MISCELLANEOUS CONTROLS.
Auto Shutdown (ASD) Relay
See AUTO SHUTDOWN (ASD) RELAY & FUEL PUMP RELAY under
MISCELLANEOUS CONTROLS.
Distributorless Ignition System (DIS)
See DISTRIBUTORLESS IGNITION SYSTEM (DIS) under IGNITION
SYSTEM.
Evaporative Canister Purge Control Solenoid (EVAP-CPCS)
See EVAPORATIVE (EVAP) EMISSIONS SYSTEM under EMISSION
SYSTEMS.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Relay
See AUTO SHUTDOWN (ASD) RELAY & FUEL PUMP RELAY under
MISCELLANEOUS CONTROLS.
Generator
See GENERATOR under MISCELLANEOUS CONTROLS.
Idle Air Control (IAC) Motor
See IDLE SPEED under FUEL SYSTEM.
Ignition Coil
See IGNITION SYSTEM.
In-Tank Fuel Pump
See FUEL DELIVERY under FUEL SYSTEM.
Limp-In Mode
See LIMP-IN MODE under MISCELLANEOUS CONTROLS.
Malfunction Indicator Light (MIL)
See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.
Radiator Fan Relay
See RADIATOR FAN RELAY under MISCELLANEOUS CONTROLS.
Serial Communications Interface (SCI) Transmit
See SERIAL COMMUNICATIONS INTERFACE (SCI) under SELF-
DIAGNOSTIC SYSTEM.
Shift Indicator Light
See SHIFT INDICATOR LIGHT under MISCELLANEOUS CONTROLS.
Speed Control Servo
See SPEED CONTROL SERVO under MISCELLANEOUS CONTROLS.
Tachometer
See TACHOMETER under MISCELLANEOUS CONTROLS.
Torque Converter Clutch (TCC) Solenoid
See TORQUE CONVERTER CLUTCH (TCC) SOLENOID under
MISCELLANEOUS CONTROLS.

Transmission Governor Pressure Solenoid
See TRANSMISSION GOVERNOR SOLENOID under MISCELLANEOUS
CONTROLS.
Transmission Overdrive/Override (OD/OR) Switch Indicator
Light
See TRANSMISSION OVERDRIVE/OVERRIDE (OD/OR) SWITCH INDICATOR
under MISCELLANEOUS CONTROLS.
Transmission Overdrive (OD) Solenoid
See TRANSMISSION OVERDRIVE (OD) SOLENOID under MISCELLANEOUS
CONTROLS.
FUEL SYSTEM
FUEL DELIVERY
Auto Shutdown (ASD) Relay
See AUTO SHUTDOWN (ASD) RELAY & FUEL PUMP RELAY under
MISCELLANEOUS CONTROLS.
Fuel Pressure Regulator
Fuel pressure regulator is a mechanical device, used to
maintain a constant pressure across fuel injector tip. Spring and
rubber diaphragm will move from an open to closed position keeping
fuel pressure constant. Excess fuel is returned to fuel tank.
Regulator is located in in-tank fuel pump module. Regulator
includes an internal fuel filter. Excess fuel is routed directly into
fuel tank without using a return line. See Fig. 2.
Fig. 2: Cross-Sectional View Of In-Tank Fuel Filter/Fuel Pressure
Regulator (Typical)
Courtesy of Chrysler Corp.
In-Tank Fuel Pump

Fuel pump is a positive displacement, immersible pump with a
permanent magnet electric motor. Fuel is drawn in through a separate
filter/strainer at bottom of fuel pump and pushed through filter to
fuel outlet line (to fuel injectors). Voltage to operate pump is
supplied from fuel pump relay. On some models, fuel pump relay is
activated by ASD relay.
Fuel pump module includes a combination fuel filter/fuel
pressure regulator, fuel pump reservoir, a separate in-tank fuel
filter, pressure relief/rollover valve, fuel gauge sending unit and
fuel supply line. See Fig. 3.
Fig. 3: Identifying Fuel Pump Module Components (Typical)
Courtesy of Chrysler Corp.
FUEL CONTROL
Fuel Injectors
Fuel injectors are electric solenoid valves controlled by
PCM. PCM determines when and length of time (pulse width) injectors
should operate by switching ground path on and off. During start-up,
battery voltage is supplied to injectors through ASD relay. On some
models, battery voltage is supplied by charging system once engine is

operating. When ground is supplied to injector by PCM, armature and
pintle inside injector move a short distance against spring and open a
small orifice. Since fuel is under high pressure, a fine spray is
developed.
Modes Of Operation
As input signals to PCM change, PCM adjusts its response to
output devices. Modes of operation come in 2 types, open loop and
closed loop. In open loop mode, PCM is not using input from HO2S and
is responding to preset programming to determine injector pulse width
and ignition timing. In closed loop mode, PCM adjusts ignition timing
and uses input from HO2S to fine tune injector pulse width.
The following inputs may be used to determine PCM mode:
* A/C Control Positions
* A/C Switch
* Battery Voltage
* Brake Switch
* Camshaft Position (CMP) Sensor
* Crankshaft Position (CKP) Sensor
* Engine Coolant Temperature (ECT) Sensor
* Engine Speed (RPM)
* Heated Oxygen Sensor (HO2S)
* Intake Air Temperature (IAT) Sensor
* Manifold Absolute Pressure (MAP) Sensor
* Park/Neutral (P/N) Switch
* Starter Relay
* Throttle Position (TP) Sensor
* Vehicle Speed Sensor (VSS)
From these inputs, PCM determines which mode vehicle is in
and responds appropriately. Not all inputs are used in all modes or by
all models. Modes of operation are:
* Ignition Switch On (Engine Not Running) - This is an open
loop mode. PCM pre-positions IAC motor based on ECT sensor
input. PCM determines atmospheric pressure from MAP sensor
and determines basic fuel strategy. PCM modifies fuel
strategy according to IAT sensor, ECT sensor and TP sensor
inputs. PCM activates ASD relay, which in turn activates fuel
pump for only 2 seconds unless engine is cranked. PCM also
energizes HO2S heater element for approximately 2 seconds
unless engine is cranked.
* Engine Start-Up - This is an open loop mode. When starter is
engaged, PCM receives input from battery voltage, ignition
switch, CKP sensor, CMP sensor, ECT sensor, IAT sensor, MAP
sensor and TP sensor. Based on these inputs, voltage is
applied to fuel injectors with PCM controlling injection
sequence, rate, and pulse width. PCM provides ground for
injectors to fire in proper order.
PCM determines proper ignition timing according to input
received from CKP sensor. If PCM does not receive CKP sensor signal
within 3 seconds after engine begins cranking, fuel injection system
is shut down and a Diagnostic Trouble Code (FTC) is set in PCM memory.\
* Engine Warm-Up - This is an open loop mode. PCM determines
injector pulse width using input information from battery
voltage, CKP sensor, CMP sensor, ECT sensor, IAT sensor, MAP
sensor and TP sensor. PCM also monitors A/C request and P/N
switch (A/T only) for fuel calculation. PCM controls engine
idle speed through IAC motor. PCM controls ignition timing
based on CKP sensor input.

PCM also operates A/C compressor clutch (if A/C is requested)\
through A/C clutch relay. When engine reaches operating temperature,
vehicle will go into idle mode and PCM will begin monitoring HO2S
input and go into closed loop operation.
* Idle - When engine is at operating temperature, this is a
closed loop mode. In idle mode, PCM now adds HO2S signal to
array of inputs used in ENGINE WARM-UP mode. PCM maintains
correct air/fuel ratio by adjusting injector pulse width and
ignition timing. PCM also controls A/C clutch operation (if
A/C is requested).
* Cruise - When engine is at operating temperature, this is a
closed loop mode. Using information from A/C switch, battery
voltage, CKP sensor, ECT sensor, IAT sensor, MAP sensor and
CMP sensor. PCM also monitors A/C request and P/N switch (A/T
only), TP sensor and VSS signals for fuel calculation. PCM
monitors HO2S and adjusts air/fuel ratio as needed. PCM
controls engine idle speed through IAC motor. PCM controls
spark advance as necessary.
* Acceleration - This is an open loop mode. When PCM
recognizes an abrupt increase in throttle position or
manifold pressure as a demand for increased engine output, it
increases injector pulse width in response to increased fuel
demand. HO2S signals are ignored.
* Deceleration - This is an open loop mode when engine is at
operating temperature and under deceleration. When PCM
receives inputs signaling a closed throttle and an abrupt
decrease in manifold pressure, it reduces injector pulse
width to lean air/fuel mixture. Under certain RPM and closed
throttle position conditions, HO2S signals are ignored and
PCM cuts off fuel injection until idle speed is reached. PCM
also drives IAC motor for smooth transition to idle mode.
* Wide Open Throttle - This is an open loop mode. When PCM
senses wide open throttle, it grounds fuel injectors in
sequence, it ignores HO2S input and it controls pulse width
to supply a pre-determined amount of additional fuel. PCM
also adjusts spark advance and disengages A/C clutch for
approximately 15 seconds.
* Ignition Switch Off - This is an open loop mode. PCM drives
IAC motor into position in anticipation of next start-up. All
outputs are turned off, no inputs are monitored and PCM shuts
down.
Sequential Fuel Injection (SFI)
Individual, electrically pulsed injectors (one per cylinder)
are located in intake manifold runners. These injectors are next to
intake valves in intake manifold. PCM controls injection timing based
on crankshaft position signal input. PCM regulates air/fuel mixture by
length of time injector stays open (pulse width) based on inputs from
HO2S, ECT sensor, MAP and other sensors.
IDLE SPEED
NOTE: DO NOT attempt to correct a high idle speed condition by
turning factory sealed throttle body throttle plate set
screw. This will not change idle speed of warm engine, but
may cause cold start problems due to restricted airflow.
Idle Air Control (IAC) Motor
IAC motor adjusts idle speed to compensate for engine load
and ambient temperature by adjusting amount of air flowing through by-
pass in back of throttle body. PCM uses ECT sensor, VSS, TP sensor and