1999 DODGE RAM Service Repair Manual

operator's foot off accelerator pedal, S/C compensates for excessive
S/C cable slack. If lift foot sets are continually used, speed control
overshoot/undershoot condition will develop.
To "unlearn" overshoot/undershoot condition, operator must
press and release set button while maintaining desired speed with
accelerator pedal, then turn S/C switch to OFF position after waiting
10 seconds. This procedure must be repeated 10-15 times to completely
unlearn overshoot/undershoot condition.
COMPONENT TESTS
WARNING: Vehicle is equipped with an air bag. Air bag must be
deactivated before servicing speed control components on or
around steering column. See appropriate AIR BAG RESTRAINT
SYSTEMS article.
NOTE: For component locations, See COMPONENT LOCATIONS. For
connector terminal identification, see CONNECTOR
IDENTIFICATION. For wiring diagram, see WIRING DIAGRAMS.
BRAKE SWITCH
Disconnect brake switch 6-pin connector. Using an ohmmeter,
check for continuity at brake switch. See Fig. 1. If continuity is not
as specified in BRAKE SWITCH CONTINUITY table, check brake switch
adjustment. See BRAKE SWITCH under REMOVAL & INSTALLATION. If brake
switch adjustment is okay, replace defective brake switch.
BRAKE SWITCH CONTINUITY








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Switch Plunger  Check Between  Continuity 


Position  Terminals  










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Released  5 & 6  Yes 










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Depressed  1 & 2  Yes 











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 3 & 4  Yes 











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SPEED CONTROL SERVO
1) Start engine. Disconnect Speed Control (S/C) servo 4-pin
connector. Turn S/C on. Using a voltmeter, check voltage at S/C servo
connector terminal No. 3 (Dark Blue/Red wire). Battery voltage should
exist when brake pedal is not depressed. If battery voltage exists, go
to next step. If battery voltage does not exist, check circuit between
brake switch and S/C servo. See WIRING DIAGRAMS.
2) Connect a jumper wire between S/C servo pin No. 3 and S/C
servo connector terminal No. 3. Check voltage at S/C servo pins No. 1,
2 and 4. If battery voltage does not exist, replace S/C servo. If
battery voltage exists, go to next step.
3) Turn ignition off. Check for continuity between S/C servo
connector terminal No. 4 and ground. If continuity exists, test is
complete. If continuity does not exist, repair open ground circuit as
necessary.
VACUUM SUPPLY
Gasoline Engines
1) Disconnect vacuum hose at speed control servo. Install
vacuum gauge to disconnected vacuum hose. Start engine and observe

gauge. Vacuum reading should be a minimum of 10 in. Hg. Turn engine
off. Vacuum should continue to hold at a minimum of 10 in. Hg.
2) If vacuum is not as specified, check for kinked or leaking
vacuum lines, defective check valve, defective vacuum reservoir or
poor engine performance. If no problems are found, check speed control
servo. See SPEED CONTROL SERVO.
Diesel Engines
1) Disconnect vacuum hose at speed control servo. Install
vacuum gauge to disconnected vacuum hose. Start engine and observe
gauge. Vacuum reading should be a minimum of 25 in. Hg. A vacuum
reservoir is not used on diesel vehicles.
2) If vacuum is not as specified, disconnect vacuum supply
hose from vacuum pump. Install vacuum gauge to vacuum pump. Start
engine and observe gauge. If vacuum reading is not 25 in. Hg or more,
replace vacuum pump. If vacuum reading 25 in. Hg or more, go to next
step.
3) Check all vacuum hoses to speed control servo, vacuum pump
and heater-A/C system for leaks. Check vacuum check valve for leaks
and proper operation. Vacuum check valve is located in vacuum hose
between speed control servo and vacuum pump. If no problems are found,
check speed control servo. See SPEED CONTROL SERVO.
CONNECTOR IDENTIFICATION
Fig. 1: Identifying Brake Switch Terminals
Courtesy of Chrysler Corp.

Fig. 2: Identifying Brake Switch Harness Connector Terminals
Courtesy of Chrysler Corp.
Fig. 3: Identifying Powertrain Control Module (PCM) Connector
Terminals
Courtesy of Chrysler Corp.

Fig. 4: Identifying Speed Control (S/C) Servo Connector Terminals
Courtesy of Chrysler Corp.
SELF-DIAGNOSTIC SYSTEM
WARNING: Vehicle is equipped with an air bag. Air bag must be
deactivated before servicing speed control components on or
around steering column. See AIR BAG RESTRAINT SYSTEMS -
TRUCKS article.
SERVICE PRECAUTIONS
Before proceeding with diagnosis, the following precautions
must be followed:
* When using Diagnostic Trouble Code (FTC) tests for diagnosis,
DO NOT skip any steps, or incorrect diagnosis may result.
Always perform indicated verification procedure after repairs are

made.
* When using a jumper wire, ensure either jumper wire or
circuit is fuse-protected.
* Before disconnecting connector from any control module,
ensure ignition is off before removing connector.
* When checking voltage or continuity at any control module,
probe connector for control module from pin side. DO NOT
backprobe connector or probe wires through insulation.
* DO NOT cause short circuits when performing electrical tests.
This will set additional Diagnostic Trouble Codes (DTCs),
making diagnosis of original problem more difficult.
* Use specified test equipment when performing electrical
tests.
RETRIEVING DIAGNOSTIC TROUBLE CODES
NOTE: Self-diagnostic tests are written specifically for Chrysler's
Diagnostic Readout Box (DRB). If using a generic scan tool,
ensure it is OBD-II certified. A generic scan tool may not be
capable of performing all necessary test functions.
Ensure battery is fully charged. Turn ignition off. Connect
scan tool to Data Link Connector (DLC). DLC is located under left side\
of instrument panel. Turn ignition on. Using scan tool manufacturer's
instructions, record all DTCs displayed on scan tool. If ant DTCs are
retrieved, perform appropriate test under DIAGNOSTIC TESTS. Once all
repairs are made, clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES.
If no DTCs are retrieved and fault still exists, go to CHECKING SPEED
CONTROL OPERATION under SYSTEM TESTS.
CLEARING DIAGNOSTIC TROUBLE CODES
Ensure ignition is off. Connect scan tool to DLC. Turn
ignition on. Using screen prompts on scan tool, erase DTCs from PCM.
DIAGNOSTIC TESTS
FTC P0720: LOW OUTPUT SPEED SENSOR (OSS) RPM MORE THAN 15 MPH
FTC P0720 will set if output shaft speed is less than 60 RPM
for 2.6 seconds when vehicle speed is more than 15 MPH.
Possible Causes:
* Defective Output Speed Sensor (OSS).
* OSS signal circuit open or shorted.
* OSS ground circuit open or shorted.
* Park/Neutral Position (PNP) switch FTC present.
* Defective PNP switch.
* Defective PCM.
1) Turn ignition on. Using scan tool, read DTCs. If FTC
specific good trip is displayed and equal to zero, go to next step. If
FTC specific good trip is equal to more than zero, go to step 13).
2) If there are any Park/Neutral Position (PNP) switch DTCs,\
repair PNP switch FTC first. Perform TEST VER-5A under VERIFICATION
TESTS. If there are no PNP switch DTCs, go to next step.
3) Using scan tool, read PNP switch state. While observing
scan tool, shift transmission through all positions. If scan tool did
not display P/N and D/R in correct positions, repair PNP switch or
circuit as necessary. Perform TEST VER-5A under VERIFICATION TESTS. If

scan tool displayed P/N and D/R in correct positions, go to next step.
4) Raise drive wheels and support vehicle, allowing wheels to
spin. Using scan tool, erase DTCs. Start engine. Using scan tool, read
Output Speed Sensor (OSS). Shift transmission into first gear. While
observing scan tool, allow wheels to spin at a speed less than 15 MPH.
If scan tool displays OSS more than 60 RPM, go to next step. If scan
tool displays OSS 60 RPM or less, go to step 7).
5) While wheels are spinning, wiggle wiring between OSS and
PCM. If OSS reading dropped while wiggling, repair intermittent short
or open circuit. Perform TEST VER-5A under VERIFICATION TESTS. If OSS
reading did not drop, go to next step.
6) Using scan tool, erase DTCs. Road test vehicle. Read DTCs.
If FTC P0720 returns, replace PCM. Perform TEST VER-5A under
VERIFICATION TESTS. If FTC P0720 did not return, go to step 13).
7) Turn ignition off. Disconnect PCM. Inspect connectors.
Clean or repair as necessary. Using an ohmmeter, measure resistance
between ground and OSS signal circuit at PCM connector C2, terminal
No. 28 (Light Green/Black wire on Ram Pickup; Light Green/White wire
on all other models). If resistance is less than 5 ohms, repair short
to ground. Perform TEST VER-5A under VERIFICATION TESTS.
8) Using an ohmmeter, measure resistance between ground and
OSS ground circuit at PCM connector C2, terminal No. 25 (Dark
Blue/Black wire). If resistance is less than 5 ohms, repair short to
ground. Perform TEST VER-5A under VERIFICATION TESTS. If resistance is
5 ohms or more, go to next step.
9) Disconnect OSS. Using an ohmmeter, measure resistance
across OSS terminals. If resistance is not 300-1200 ohms, replace OSS.
Perform TEST VER-5A under VERIFICATION TESTS. If resistance is 300-
1200 ohms, go to next step.
10) Using an ohmmeter, measure resistance of OSS signal
circuit between PCM connector C2, terminal No. 28 and OSS connector
(Light Green/Black wire on Ram Pickup; Light Green/White wire on all
other models). If resistance is more than 5 ohms, repair open circuit.
Perform TEST VER-5A under VERIFICATION TESTS. If resistance is 5 ohms
or less, go to next step.
11) Using an ohmmeter, measure resistance of OSS ground
circuit between PCM connector C2, terminal No. 25 and OSS connector
(Dark Blue/Black wire). If resistance is more than 5 ohms, repair open\
circuit. Perform TEST VER-5A under VERIFICATION TESTS. If resistance
is 5 ohms or less, go to next step.
12) Reconnect OSS. Using an ohmmeter, measure resistance
between PCM connector C2, terminals No. 25 (Dark Blue/Black wire) and
No. 28 (Light Green/Black wire on Ram Pickup; Light Green/White wire
on all other models). If resistance is 300-1200 ohms, replace PCM.
Perform TEST VER-5A under VERIFICATION TESTS. If resistance is not
300-1200 ohms, go to next step.
13) Inspect wiring and connectors. repair as necessary.
Perform TEST VER-5A under VERIFICATION TESTS. If wiring and connectors
are okay, go to next step.
14) Conditions required to set FTC are not present at this
time. Check freeze frame data to determine conditions when FTC was
set. Raise drive wheels and support vehicle, allowing wheels to spin.
Using scan tool, read OSS. Shift transmission into first gear. While
observing scan tool, allow wheels to spin at a speed less than 15 MPH.
Wiggle wiring between OSS and PCM. If OSS reading dropped while
wiggling, repair intermittent short or open circuit. Perform TEST VER-
5A under VERIFICATION TESTS. If OSS reading did not drop, no problem
is indicated at this time.
FTC P1595: SPEED CONTROL SOLENOID CIRCUITS
Speed Control (S/C) solenoid circuits are monitored when
engine is running, S/C switch is on and battery voltage is more than

10.4 volts. FTC P1595 will set if vacuum and vent solenoids do not
respond when actuated by PCM.
Possible Causes:
* Ground circuit open.
* S/C brake switch output circuit open.
* S/C power supply circuit open or shorted.
* S/C servo defective.
* S/C vacuum solenoid control circuit open or shorted.
* S/C vent solenoid control circuit open or shorted.
* Brake switch defective or out of adjustment.
* Defective PCM.
NOTE: For component locations, see COMPONENT LOCATIONS. For
connector terminal identification, see CONNECTOR
IDENTIFICATION. For wiring diagram, see WIRING DIAGRAMS.
1) Turn ignition on. Turn Speed Control (S/C) on. Using scan\
tool, actuate S/C vent solenoid. If speed control servo clicks, go to
next step. If S/C servo does not click, go to step 7).
2) Using scan tool, actuate S/C vacuum solenoid. If S/C servo
clicks, go to next step. If S/C servo does not click, go to step 6).
3) Turn ignition on. Using scan tool, actuate S/C vacuum
solenoid. Wiggle wiring harness between S/C servo and brake switch to
PCM while scan tool is still actuating speed control vacuum solenoid.
If wiggling did not cause an interruption of S/C servo actuation, go
to next step. If wiggling caused an interruption of S/C servo
actuation, repair wiring harness as necessary. Perform TEST VER-4A
under VERIFICATION TESTS.
4) Turn ignition off. Inspect S/C wiring and connectors.
Clean or repair as necessary. Perform TEST VER-4A under VERIFICATION
TESTS. If wiring and connectors are okay, go to next step.
5) Using scan tool, actuate S/C vent solenoid. Wiggle wiring
harness between S/C servo and brake switch to PCM while scan tool is
still actuating speed control vacuum solenoid. If wiggling did not
cause interruption of S/C servo actuation, test is complete. If
wiggling caused interruption of S/C servo actuation, repair wiring
harness as necessary. Perform TEST VER-4A under VERIFICATION TESTS.
6) Using scan tool, actuate S/C vent solenoid. Wiggle wiring
harness between S/C servo and brake switch to PCM while scan tool is
still actuating speed control vacuum solenoid. If wiggling did not
cause interruption of S/C servo actuation, go to next step. If
wiggling caused interruption of S/C servo actuation, repair wiring
harness as necessary. Perform TEST VER-4A under VERIFICATION TESTS.
NOTE: Ensure brake pedal is not depressed during the following
steps.
7) Turn ignition off. Disconnect S/C servo 4-pin connector.
Inspect all related wiring and connectors and repair as necessary.
Turn ignition on. Turn S/C switch on. Using a 12-volt test light,
probe brake switch output circuit at S/C servo connector terminal No.
3 (Dark Blue/Red wire). If test light is illuminated and bright, go to\
next step. If test light is dim or not illuminated, go to step 13).
8) Turn ignition off. Using an ohmmeter, check resistance of
ground circuit at S/C servo connector terminal No. 4 (Black wire). If
resistance is 5 ohms or more, repair open ground circuit. Perform TEST
VER-4A under VERIFICATION TESTS. If resistance is less than 5 ohms, go
to next step.
9) Disconnect PCM. Inspect connectors. Clean or repair as
necessary. Using an ohmmeter, measure resistance between ground and
S/C vacuum solenoid control circuit at S/C servo connector terminal

No. 1 (Tan/Red wire). If resistance is less than 5 ohms, repair short
to ground. Perform TEST VER-4A under VERIFICATION TESTS. If resistance
is 5 ohms or more, go to next step.
10) Using an ohmmeter, check resistance between ground and
S/C vent solenoid control circuit at S/C servo connector terminal No.
2 (Light Green/Red wire). If resistance is less than 5 ohms, repair
short to ground. Perform TEST VER-4A under VERIFICATION TESTS. If
resistance is 5 ohms or more, go to next step.
11) Using an ohmmeter, measure resistance of S/C vacuum
solenoid control circuit between S/C servo connector terminal No. 1
and PCM connector C3, terminal No. 4 (Tan/Red wire). If resistance is
5 ohms or more, repair open circuit. Perform TEST VER-4A under
VERIFICATION TESTS. If resistance is less than 5 ohms, go to next
step.
12) Using an ohmmeter, check resistance of S/C vent solenoid
control circuit between S/C servo connector terminal No. 2 and PCM
connector C3, terminal No. 5 (Light Green/Red wire). If resistance is
5 ohms or more, repair open circuit. Perform TEST VER-4A under
VERIFICATION TESTS. If resistance is less than 5 ohms, replace S/C
servo. Perform TEST VER-4A under VERIFICATION TESTS.
13) Using an ohmmeter, check resistance between ground and
brake switch output circuit at S/C servo connector terminal No. 3
(Dark Blue/Red wire). If resistance is less than 5 ohms, repair short
to ground. Perform TEST VER-4A under VERIFICATION TESTS. If resistance
is 5 ohms or more, go to next step.
14) Reconnect PCM. Disconnect brake switch connector. Turn
ignition on. Turn S/C on. Using a 12-volt test light, probe S/C power
supply circuit at brake switch connector terminal No. 3 (Yellow/Red
wire). If test light is illuminated and bright, go to next step. If
test light is not illuminated or dim, go to step 17).
15) Turn ignition off. Using an ohmmeter, check resistance of
S/C brake switch output circuit between S/C servo connector terminal
No. 3 and brake switch connector terminal No. 4 (Dark Blue/Red wire).
If resistance is 5 ohms or more, repair open circuit. Perform TEST
VER-4A under VERIFICATION TESTS. If resistance is less than 5 ohms, go
to next step.
16) Check brake switch adjustment. See BRAKE SWITCH under
REMOVAL & INSTALLATION. Adjust as necessary. Perform TEST VER- 4A
under VERIFICATION TESTS. If brake switch adjustment is okay, replace
brake switch. Perform TEST VER-4A under VERIFICATION TESTS.
17) Turn ignition off. Disconnect PCM. Inspect connectors.
Clean or repair as necessary. Using an ohmmeter, measure resistance of
S/C power supply circuit between PCM connector C3, terminal No. 11 and
brake switch connector terminal No. 3 (Yellow/Red wire). If resistance\
is 5 ohms or more, repair open circuit. Perform TEST VER-4A under
VERIFICATION TESTS. If resistance is less than 5 ohms, replace PCM.
Perform TEST VER-4A under VERIFICATION TESTS.
FTC P1596: SPEED CONTROL SWITCH ALWAYS HIGH
FTC P1596 will set if an open circuit is detected in Speed
Control (S/C) switch circuit when ignition is on.
Possible Causes:
* Defective clockspring.
* S/C switch ground circuit open.
* Defective ON/OFF switch.
* Defective PCM.
* S/C switch signal circuit open or shorted to voltage.
NOTE: For component locations, see COMPONENT LOCATIONS. For
connector terminal identification, see CONNECTOR