2002 DODGE RAM check engine

FOG LAMP
DIAGNOSIS AND TESTING - FOG LAMP
CONDITION POSSIBLE CAUSES CORRECTION
FOG LAMPS ARE DIM
WITH ENGINE IDLING OR
IGNITION TURNED OFF.1. Loose or corroded battery cables. 1. Clean and secure battery cable clamps
and posts.
2. Loose or worn generator drive
belt.2. Adjust or replace generator drive belt.
3. Charging system output too low. 3. Test and repair charging system.
4. Battery has insufficient charge. 4. Test battery state-of -charge.
5. Battery is sulfated or shorted. 5. Load test battery.
6. Poor lighting circuit Z33-ground. 6. Test for voltage drop across Z33-ground
locations.
FOG LAMP BULBS BURN
OUT FREQUENTLY1. Charging system output too high. 1. Test and repair charging system.
2. Loose or corroded terminals or
splices in circuit.2. Inspect and repair all connectors and
splices.
FOG LAMPS ARE DIM
WITH ENGINE RUNNING
ABOVE IDLE1. Charging system output too low. 1. Test and repair charging system.
2. Poor lighting circuit Z33-ground. 2. Test for voltage drop across Z33-ground
locations.
3. High resistance in fog lamp circuit. 3. Test amperage draw of fog lamp circuit.
FOG LAMPS FLASH
RANDOMLY1. Poor lighting circuit Z33-ground. 1. Test for voltage drop across Z33-ground
locations.
2. High resistance in fog lamp circuit. 2. Test amperage draw of fog lamp circuit.
3. Faulty fog lamp switch. 3. Replace fog lamp switch.
4. Loose or corroded terminals or
splices in circuit.4. Inspect and repair all connectors and
splices.
FOG LAMPS DO NOT
ILLUMINATE1. Blown fuse for fog lamp. 1.Trace short and replace fuse.
2. No Z33-ground at fog lamps. 2. Repair circuit ground.
3. Faulty fog lamp switch. 3. Replace fog lamp switch.
4. Broken connector terminal or wire
splice in fog lamp circuit.4. Repair connector terminal or wire splice.
5. Defective or burned out bulb. 5. Replace bulb.
FOG LAMPS ARE
INOPERATIVE AND FOG
LAMP INDICATOR LIGHT
ALWAYS STAYS ON.1. Fog lamp/DRL* feed shorted to
ground.1. Check wiring circuit from fog lamp/DRL*
fuse to fog lamp. Trace short circuit in
wiring and repair.
FOG LAMPS ARE
INOPERATIVE AND FOG
LAMP INDICATOR LIGHT
IS ILLUMINATED.1. Fog lamp/DRL* fuse defective. 1. Trace short circuit and replace fuse.
2. Open circuit from fog lamp fuse to
fog lamp.2. Check wiring circuit from fog lamp/DRL*
fuse to fog lamp. Trace open circuit in
wiring and repair.
8L - 10 LAMPS/LIGHTING - EXTERIORBR/BE

DIAGNOSIS AND TESTING - HEADLAMP
A good ground is necessary for proper lighting
operation. Grounding is provided by the lamp socket
when it comes in contact with the metal body, or
through a separate ground wire.
Always begin any diagnosis by testing all of the
fuses and circuit breakers in the system. For com-plete circuit diagrams, refer to the appropriate wir-
ing information. The wiring information includes
wiring diagrams, proper wire and connector repair
procedures, details of wire harness routing and
retention, connector pin-out information and location
views for the various wire harness connectors, splices
and grounds.
CONDITION POSSIBLE CAUSES CORRECTION
HEADLAMPS ARE DIM
WITH ENGINE IDLING1. Loose or corroded battery cables. 1. Clean and secure battery cable clamps
and posts.
OR IGNITION TURNED
OFF2. Loose or worn generator drive
belt.2. Adjust or replace generator drive belt.
3. Charging system output too low. 3. Test and repair charging system.
4. Battery has insufficient charge. 4. Test battery state-of -charge.
5. Battery is sulfated or shorted. 5. Load test battery.
6. Poor lighting circuit Z3-ground. 6. Test for voltage drop across Z3-ground
locations.
7. Both headlamp bulbs defective. 7. Replace both headlamp bulbs.
HEADLAMP BULBS BURN
OUT1. Charging system output too high. 1. Test and repair charging system.
FREQUENTLY 2. Loose or corroded terminals or
splices in circuit.2. Inspect and repair all connectors and
splices.
HEADLAMPS ARE DIM
WITH ENGINE RUNNING1. Charging system output too low. 1. Test and repair charging system.
ABOVE IDLE* 2. Poor lighting circuit Z3-ground. 2. Test for voltage drop across Z3-ground
locations.
3. High resistance in headlamp
circuit.3. Test amperage draw of headlamp circuit.
4. Both headlamp bulbs defective. 4. Replace both headlamp bulbs.
HEADLAMPS FLASH
RANDOMLY1. Poor lighting circuit Z3-ground. 1. Test for voltage drop across Z3-ground
locations.
2. High resistance in headlamp
circuit.2. Test amperage draw of headlamp circuit.
Should not exceed 30 amps.
3. Faulty headlamps switch circuit
breaker.3. Replace headlamp switch.
4. Loose or corroded terminals or
splices in circuit.4. Inspect and repair all connectors and
splices.
HEADLAMPS (HIGH &
LOW) DO NOT
ILLUMINATE1. No voltage at either headlamp. 1. Voltage should always be present. Trace
short circuit and replace BOTH headlamp
fuses. Check wiring circuit from Right
headlamp fuse to headlamp. (Repeat for
Left side)
8L - 14 LAMPS/LIGHTING - EXTERIORBR/BE
HEADLAMP (Continued)

LAMPS/LIGHTING - INTERIOR
TABLE OF CONTENTS
page page
LAMPS/LIGHTING - INTERIOR
SPECIFICATIONS
INTERIOR LAMPS.....................33
DOME LAMP
REMOVAL.............................34
INSTALLATION.........................34
DOOR AJAR SWITCH
DESCRIPTION.........................34
DIAGNOSIS AND TESTING - DOOR AJAR
SWITCH............................34
REMOVAL.............................35
INSTALLATION.........................35GLOVE BOX LAMP AND SWITCH
REMOVAL.............................35
INSTALLATION.........................36
READING LAMP
DESCRIPTION.........................36
OPERATION...........................36
REMOVAL.............................36
INSTALLATION.........................37
VANITY LAMP
REMOVAL.............................37
INSTALLATION.........................37
LAMPS/LIGHTING - INTERIOR
SPECIFICATIONS
INTERIOR LAMPS
LAMP BULB
A/C HEATER CONTROL 158
ASH RECEIVER 161
CIGAR LIGHTER 161
HEADLAMP SWITCH 158
HEATER CONTROL 158
INSTRUMENT CLUSTER PC194
RADIO ASC
AIRBAG HIGH LINE PC194
AIRBAG LOW LINE PC74
ANTI-LOCK BRAKE PC74
BATTERY VOLTAGE PC194
BRAKE WARNING PC194LAMP BULB
CHECK ENGINE PC74
ENGINE OIL PRESSURE PC74
FOUR WHEEL DRIVE PC194
HIGH BEAM PC194
LOW FUEL PC194
LOW WASHER FLUID PC74
MAINTENANCE
REQUIREDPC74
MESSAGE CENTER PC194
SEAT BELT PC74
TURN SIGNAL PC194
UPSHIFT PC74
DOME 1004
GLOVE COMPARTMENT 1891
VANITY MIRROR LAMP P/N 6501966
BR/BELAMPS/LIGHTING - INTERIOR 8L - 33

AMBIENT TEMP SENSOR
DESCRIPTION
Ambient air temperature is monitored by the com-
pass mini-trip computer module through the ambient
temperature sensor. The ambient temperature sensor
is a variable resistor mounted to a bracket that is
secured with a screw to the underside of the hood
panel near the hood latch striker in the engine com-
partment (Fig. 8).
For complete circuit diagrams, refer toOverhead
Consolein the Contents of Wiring Diagrams. The
ambient temperature sensor cannot be adjusted or
repaired and, if faulty or damaged, it must be
replaced.
OPERATION
The ambient temperature sensor is a variable
resistor that operates on a five-volt reference signal
sent to it by the compass mini-trip computer module.
The resistance in the sensor changes as temperature
changes, changing the return circuit voltage to the
compass mini-trip computer module. Based upon the
resistance in the sensor, the compass mini-trip com-
puter module senses a specific voltage on the return
circuit, which it is programmed to correspond to a
specific temperature.
DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR
The thermometer function is supported by the
ambient temperature sensor, a wiring circuit, and a
portion of the compass mini-trip computer module. If
any portion of the ambient temperature sensor cir-
cuit fails, the compass/thermometer display function
will self-diagnose the circuit. If 55É C (131É F)
appears in the display, the sensor is being exposed to
temperatures above 55É C (131É F), or the sensor cir-
cuit is shorted. If ±40É C (±40É F) appears in the dis-
play, the sensor is being exposed to temperatures
below ±40É C (±40É F), or the sensor circuit is open.
The ambient temperature sensor circuit can also be
diagnosed using the following Sensor Test, and Sen-
sor Circuit Test. If the temperature sensor and cir-
cuit are confirmed to be OK, but the temperature
display is inoperative or incorrect, refer toDiagnosis
and Testing the Compass Mini-Trip Computer.
For complete circuit diagrams, refer toWiring Dia-
grams.
SENSOR TEST
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire har-
ness connector.(2) Measure the resistance of the ambient temper-
ature sensor. At ±40É C (±40É F), the sensor resis-
tance is 336 kilohms. At 55É C (131É F), the sensor
resistance is 2.488 kilohms. The sensor resistance
should read between these two values. If OK, refer to
theSensor Circuit Test below. If not OK, replace
the faulty ambient temperature sensor.
SENSOR CIRCUIT TEST
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire har-
ness connector and the overhead console wire har-
ness connector.
(2) Connect a jumper wire between the two termi-
nals in the body half of the ambient temperature sen-
sor wire harness connector.
(3) Check for continuity between the sensor return
circuit and the ambient temperature sensor signal
circuit cavities of the roof wire harness overhead con-
sole connector. There should be continuity. If OK, go
to Step 4. If not OK, repair the open sensor return
circuit or ambient temperature sensor signal circuit
to the ambient temperature sensor as required.
(4) Remove the jumper wire from the body half of
the ambient temperature sensor wire harness con-
nector. Check for continuity between the sensor
return circuit cavity of the roof wire harness over-
head console connector and a good ground. There
should be no continuity. If OK, go to Step 5. If not
OK, repair the shorted sensor return circuit as
required.
(5) Check for continuity between the ambient tem-
perature sensor signal circuit cavity of the roof wire
harness overhead console connector and a good
ground. There should be no continuity. If OK, refer to
Diagnosis and Testing the Compass Mini-Trip
Computerin this section. If not OK, repair the
shorted ambient temperature sensor signal circuit as
required.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Locate the ambient temperature sensor, on the
underside of the hood near the hood latch striker
(Fig. 8).
(3) Disconnect the wire harness connector from the
ambient temperature sensor connector receptacle.
(4) Remove the one screw that secures the ambient
temperature sensor bracket to the inner hood rein-
forcement.
(5) Remove the ambient temperature sensor from
the inner hood reinforcement.
8M - 12 MESSAGE SYSTEMSBR/BE

Once the speed control has been disengaged,
depressing the RES/ACCEL switch (when speed is
greater than 30 mph) restores the vehicle to the tar-
get speed that was stored in the ECM.
While the speed control is engaged, the driver can
increase the vehicle speed by depressing the RES/AC-
CEL switch. The new target speed is stored in the
ECM when the RES/ACCEL is released. The ECM
also has a9tap-up9feature in which vehicle speed
increases at a rate of approximately 2 mph for each
momentary switch activation of the RES/ACCEL
switch.
A ªtap downº feature is used to decelerate without
disengaging the speed control system. To decelerate
from an existing recorded target speed, momentarily
depress the COAST switch. For each switch activa-
tion, speed will be lowered approximately 1 mph.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - VACUUM SUPPLY
TEST
Gas Powered Engines
On gasoline powered engines: actual engine vac-
uum, a vacuum reservoir, a one-way check valve and
vacuum lines are used to supply vacuum to the speed
control servo.
(1) Disconnect vacuum hose at speed control servo
and install a vacuum gauge into the disconnected
hose.
(2) Start engine and observe gauge at idle. Vac-
uum gauge should read at least ten inches of mer-
cury.
(3) If vacuum is less than ten inches of mercury,
determine source of leak. Check vacuum line to
engine for leaks. Also check actual engine intake
manifold vacuum. If manifold vacuum does not meet
this requirement, check for poor engine performance
and repair as necessary.
(4) If vacuum line to engine is not leaking, check
for leak at vacuum reservoir. To locate and gain
access to reservoir, refer to Vacuum Reservoir Remov-
al/Installation in this group. Disconnect vacuum line
at reservoir and connect a hand-operated vacuum
pump to reservoir fitting. Apply vacuum. Reservoir
vacuum should not bleed off. If vacuum is being lost,
replace reservoir.
(5) Verify operation of one-way check valve and
check it for leaks.
(a) Locate one-way check valve. The valve is
located in vacuum line between vacuum reservoirand engine vacuum source. Disconnect vacuum
hoses (lines) at each end of valve.
(b) Connect a hand-operated vacuum pump to
reservoir end of check valve. Apply vacuum. Vac-
uum should not bleed off. If vacuum is being lost,
replace one-way check valve.
(c) Connect a hand-operated vacuum pump to
vacuum source end of check valve. Apply vacuum.
Vacuum should flow through valve. If vacuum is
not flowing, replace one-way check valve. Seal the
fitting at opposite end of valve with a finger and
apply vacuum. If vacuum will not hold, diaphragm
within check valve has ruptured. Replace valve.
Diesel Engines With Automatic Trans.
On diesel powered engines equipped with an auto-
matic transmission: an engine driven vacuum pump,
a one-way check valve and vacuum lines are used to
supply vacuum to the speed control servo. A vacuum
reservoir is not used.
(1) Disconnect vacuum hose at speed control servo
and install a vacuum gauge into the disconnected
hose.
(2) Start engine and observe gauge at idle. For
vacuum testing and vacuum specifications, refer to
Vacuum Pump OutputÐDiesel Engine in 9, Engines.
(3) If vacuum pump output is OK, determine other
source of leak. Check all vacuum lines to: speed con-
trol servo, engine vacuum pump and heating/air con-
ditioning system for leaks.
(4) Verify operation of one-way check valve and
check it for leaks.
(a) Locate one-way check valve. The valve is
located in vacuum line between speed control servo
and engine vacuum pump. Disconnect vacuum
hoses (lines) at each end of valve.
(b) Connect a hand-operated vacuum pump to
reservoir end of check valve. Apply vacuum. Vac-
uum should not bleed off. If vacuum is being lost,
replace one-way check valve.
(c) Connect a hand-operated vacuum pump to
vacuum source end of check valve. Apply vacuum.
Vacuum should flow through valve. If vacuum is
not flowing, replace one-way check valve. Seal the
fitting at opposite end of valve with a finger and
apply vacuum. If vacuum will not hold, diaphragm
within check valve has ruptured. Replace valve.
Diesel Engine With Manual Trans.
Vacuum is not used for any part of the speed con-
trol system if equipped with a diesel engine and a
manual transmission.
BR/BESPEED CONTROL 8P - 3
SPEED CONTROL (Continued)

DIAGNOSIS AND TESTING - ROAD TEST
Perform a vehicle road test to verify reports of
speed control system malfunction. The road test
should include attention to the speedometer.
If a road test verifies a system problem and the
speedometer operates properly, check for:
²A Diagnostic Trouble Code (DTC). If a DTC
exists, conduct tests per the Powertrain Diagnostic
Procedures service manual.
²A misadjusted brake (stop) lamp switch. This
could also cause an intermittent problem.
²Loose, damaged or corroded electrical connec-
tions at the servo. Corrosion should be removed from
electrical terminals and a light coating of Mopart
MultiPurpose Grease, or equivalent, applied.²Leaking vacuum reservoir.
²Loose or leaking vacuum hoses or connections.
²Defective one-way vacuum check valve.
²Secure attachment of both ends of the speed con-
trol servo cable.
²Smooth operation of throttle linkage and throttle
body air valve.
²Failed speed control servo. Do the servo vacuum
test.
CAUTION: When test probing for voltage or conti-
nuity at electrical connectors, care must be taken
not to damage connector, terminals or seals. If
these components are damaged, intermittent or
complete system failure may occur.
SPECIFICATIONS
TORQUE - SPEED CONTROL SYSTEM
DESCRIPTION N´m Ft. Lbs. In. Lbs.
Servo Mounting Bracket
Nuts8.5 - 75
Switch Module Mounting
Screws3-26
Vacuum Reservoir
Mounting Screws2.2 -
20
CABLE
DESCRIPTION
The speed control servo cable is connected between
the speed control vacuum servo diaphragm and the
throttle body control linkage.
OPERATION
This cable causes the throttle control linkage to
open or close the throttle valve in response to move-
ment of the vacuum servo diaphragm.
REMOVAL
REMOVAL - GAS ENGINES
(1) Disconnect negative battery cable at battery.
(2) Remove air cleaner (all except 8.0L V-10
engine).(3) Using finger pressure only, remove speed con-
trol cable connector at bellcrank by pushing connec-
tor off the bellcrank pin (Fig. 1) or (Fig. 2).DO NOT
try to pull connector off perpendicular to the
bellcrank pin. Connector will be broken.Fig. 1 Servo Cable at Throttle BodyÐV6/V-8 Engine
1 - VEHICLE SPEED CONTROL CABLE
8P - 4 SPEED CONTROLBR/BE
SPEED CONTROL (Continued)

(4) Squeeze 2 tabs on sides of speed control cable
at throttle body mounting bracket (locking plate) and
push out of bracket.
(5) Remove servo cable from servo. Refer to Speed
Control Servo Removal/Installation in this group.
REMOVAL - DIESEL WITH AUTO. TRANS.
(1) Disconnect both negative battery cables at both
batteries.
(2) Remove cable/lever/linkage cover. Refer to
Speed Control Servo Removal/Installation.
(3) Remove (disconnect) servo cable from servo.
Refer to Speed Control Servo Removal/Installation.
(4) Using finger pressure only, disconnect end of
servo cable from throttle lever pin by pulling forward
on connector while holding lever rearward (Fig. 3).
DO NOT try to pull connector off perpendicular
to lever pin. Connector will be broken.(5) Squeeze 2 pinch tabs (Fig. 3) on sides of speed
control cable at mounting bracket and push cable
rearward out of bracket.
(6) Remove cable from vehicle.
INSTALLATION
INSTALLATION - GAS ENGINES
(1) Install end of cable to speed control servo.
Refer to Speed Control Servo Removal/Installation.
(2) Install cable into throttle body mounting
bracket. Cable snaps into bracket.
(3) Install speed control cable connector at throttle
body bellcrank pin. Connector snaps onto pin.
(4) Connect negative battery cable to battery.
(5) Before starting engine, operate accelerator
pedal to check for any binding.
Fig. 2 Servo Cable at Throttle BodyÐV-10 Engine
1 - THROTTLE CABLE
2 - THROTTLE VALVE CABLE3 - SPEED CONTROL SERVO CABLE
BR/BESPEED CONTROL 8P - 5
CABLE (Continued)

INSTALLATION - DIESEL WITH AUTO. TRANS.
(1) Install (connect) end of speed control servo
cable to speed control servo. Refer to Speed Control
Servo Removal/Installation.
(2) Install cable through mounting hole on mount-
ing bracket. Cable snaps into bracket.
(3) Connect servo cable to throttle lever by push-
ing cable connector rearward onto lever pin while
holding lever forward.
(4) Connect negative battery cables to both batter-
ies.
(5) Before starting engine, operate accelerator
pedal to check for any binding.
(6) Install cable/lever cover.
SPEED CONTROL SERVO
DESCRIPTION
A speed control servo is not used if equipped
with both a diesel engine and a manual trans-
mission.
The servo unit consists of a solenoid valve body,
and a vacuum chamber. The solenoid valve body con-
tains three solenoids:
²Vacuum²Vent
²Dump
The vacuum chamber contains a diaphragm with a
cable attached to control the throttle linkage.
OPERATION
A speed control servo is not used if equipped
with both a diesel engine and a manual trans-
mission.
The Powertrain Control Module (PCM) controls the
solenoid valve body. The solenoid valve body controls
the application and release of vacuum to the dia-
phragm of the vacuum servo. The servo unit cannot
be repaired and is serviced only as a complete assem-
bly.
Power is supplied to the servo's by the PCM
through the brake switch. The PCM controls the
ground path for the vacuum and vent solenoids.
The dump solenoid is energized anytime it receives
power. If power to the dump solenoid is interrupted,
the solenoid dumps vacuum in the servo. This pro-
vides a safety backup to the vent and vacuum sole-
noids.
The vacuum and vent solenoids must be grounded
at the PCM to operate. When the PCM grounds the
vacuum servo solenoid, the solenoid allows vacuum
to enter the servo and pull open the throttle plate
using the cable. When the PCM breaks the ground,
the solenoid closes and no more vacuum is allowed to
enter the servo. The PCM also operates the vent sole-
noid via ground. The vent solenoid opens and closes a
passage to bleed or hold vacuum in the servo as
required.
The PCM duty cycles the vacuum and vent sole-
noids to maintain the set speed, or to accelerate and
decelerate the vehicle. To increase throttle opening,
the PCM grounds the vacuum and vent solenoids. To
decrease throttle opening, the PCM removes the
grounds from the vacuum and vent solenoids. When
the brake is released, if vehicle speed exceeds 30
mph to resume, 35 mph to set, and the RES/ACCEL
switch has been depressed, ground for the vent and
vacuum circuits is restored.
REMOVAL
REMOVAL
V-8 ENGINE
(1) Disconnect negative battery cable at battery.
(2) Disconnect electrical connector at servo (Fig. 4).
(3) Disconnect vacuum hose at servo.
(4) Disconnect servo cable at throttle body. Refer to
Servo Cable Removal/Installation in this group.
Fig. 3 Servo Cable at Throttle Lever
1 - PINCH (2) TABS
2 - CABLE MOUNTING BRACKET
3 - PINCH TABS (2)
4 - OFF
5 - THROTTLE CABLE
6 - THROTTLE LEVER
7 - THROTTLE LEVER PIN
8 - OFF
9 - CONNECTOR
10 - SPEED CONTROL CABLE
8P - 6 SPEED CONTROLBR/BE
CABLE (Continued)