Dodge Ram Truck 1500-2500-3500. Manual — part 572

OPERATION

When speed control is selected by depressing the ON switch, the PCM (the ECM with a diesel engine) allows a set
speed to be stored in its RAM for speed control. To store a set speed, depress the SET switch while the vehicle is
moving at a speed between 35 and 85 mph. In order for the speed control to engage, the brakes cannot be applied,
nor can the gear selector be indicating the transmission is in Park or Neutral.

The speed control can be disengaged manually by:

•

Stepping on the brake pedal

•

Depressing the OFF switch

•

Depressing the CANCEL switch.

•

Depressing the clutch pedal (if equipped).

NOTE: Depressing the OFF switch or turning off the ignition switch will erase the set speed stored in the
PCM (the ECM with a diesel engine).

For added safety, the speed control system is programmed to disengage for any of the following conditions:

•

An indication of Park or Neutral

•

A rapid increase rpm (indicates that the clutch has been disengaged)

•

Excessive engine rpm (indicates that the transmission may be in a low gear)

•

The speed signal increases at a rate of 10 mph per second (indicates that the coefficient of friction between
the road surface and tires is extremely low)

•

The speed signal decreases at a rate of 10 mph per second (indicates that the vehicle may have decelerated
at an extremely high rate)

Once the speed control has been disengaged, depressing the RES/ACCEL switch (when speed is greater than 30
mph) restores the vehicle to the target speed that was stored in the PCM (the ECM with a diesel engine).

While the speed control is engaged, the driver can increase the vehicle speed by depressing the RES/ACCEL
switch. The new target speed is stored in the PCM (the ECM with a diesel engine) when the RES/ACCEL is
released. The PCM (the ECM with a diesel engine) also has a

9

tap-up

9

feature in which vehicle speed increases at

a rate of approximately 2 mph for each momentary switch activation of the RES/ACCEL switch.

A “tap down” 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 activation, speed will be
lowered approximately 1 mph.

DIAGNOSIS AND TESTING

DIAGNOSIS AND TESTING - VACUUM SUPPLY TEST

3.7L / 4.7L Gas Powered Engines

3.7L/4.7L gas powered engines: actual engine vacuum, 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. Vacuum gauge should read at least ten inches of mercury.

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 reser-

voir, refer to Vacuum Reservoir Removal/Installation in this group. Disconnect vacuum line at reservoir and con-
nect 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 reservoir and engine

vacuum source. Disconnect vacuum hoses (lines) at each end of valve.

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b. Connect a hand-operated vacuum pump to reservoir end of check valve. Apply vacuum. Vacuum 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.

5.7 Gas

Vacuum is not used for any part of the speed control system if equipped with a 5.7L V-8 engine.

5.9L Diesel

Vacuum is not used for any part of the speed control system if equipped with a diesel engine.

DIAGNOSIS AND TESTING - ROAD TEST

Perform a vehicle road test to verify reports of speed control system malfunction. The road test should include atten-
tion to the speedometer. Speedometer operation should be smooth and without flutter at all speeds.

Flutter in the speedometer indicates a problem which might cause surging in the speed control system. The cause
of any speedometer problems should be corrected before proceeding. Refer to Instrument Cluster for speedometer
diagnosis.

If a road test verifies a system problem and the speedometer operates properly, check for:

•

A Diagnostic Trouble Code (DTC). If a DTC exists, conduct tests per the Powertrain Diagnostic Procedures
service manual.

•

A misadjusted brake (stop) lamp switch. This could also cause an intermittent problem.

•

Loose, damaged or corroded electrical connections at the servo (if used). Corrosion should be removed from
electrical terminals and a light coating of Mopar MultiPurpose Grease, or equivalent, applied.

•

Leaking vacuum reservoir (if used).

•

Loose or leaking vacuum hoses or connections (if used).

•

Defective one-way vacuum check valve (if used).

•

Secure attachment of both ends of the speed control servo cable (if used).

•

Smooth operation of throttle linkage (if used) and throttle body air valve.

•

Failed speed control servo (if used). Do the servo vacuum test.

CAUTION: When test probing for voltage or continuity 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

DESCRIPTION

N-m

Ft. Lbs.

In. Lbs.

Servo Mounting Bracket-

to-Servo Nuts

7

-

60

Servo Mounting Bracket-

to-Battery Tray Screws

4

-

30

Speed Control Switch

Mounting Screws

1.7

-

15

Vacuum Reservoir

Mounting Nuts

3

-

20

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SPEED CONTROL

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CABLE-SPEED CONTROL

DESCRIPTION

The speed control servo cable is connected between the speed control vacuum servo diaphragm and the throttle
body control linkage. This cable is used only with 3.7L/4.7L gas powered engines only.

A speed control servo cable is not used if equipped with either a 5.9L diesel engine, or any 5.7L engine.

OPERATION

This cable causes the throttle control linkage to open or close the throttle valve in response to movement of the
vacuum servo diaphragm.

REMOVAL

3.7L / 4.7L GAS

1. Disconnect negative battery cable at battery.

2. Remove air intake tube at top of throttle body.

The accelerator cable must be partially removed to
gain access to speed control cable.

3. Hold throttle in wide open position. While held in

this position, slide throttle cable pin (1) from throttle
body bellcrank.

4. Using a pick or small screwdriver (3), press release

tab (2) to release plastic cable mount (4) from
bracket. Press on tab only enough to release
cable from bracket. If tab is pressed too much,
it will be broken. Slide plastic mount (4) towards
right side of vehicle to remove throttle cable from
throttle body bracket.

5. Using finger pressure only, disconnect servo cable connector (2) at throttle body bellcrank pin by pushing con-

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nector off bellcrank pin towards front of vehicle. DO
NOT try to pull connector off perpendicular to
the bellcrank pin. Connector will be broken.

6. Slide speed control cable plastic mount (2) towards

right of vehicle to remove cable (3) from throttle
body bracket (1).

7. Remove servo cable from servo. Refer to Servo

Removal/Installation.

INSTALLATION

3.7L / 4.7L Gas

1. Install end of cable to speed control servo. Refer to Servo Removal/Installation.

2. Slide speed control cable plastic mount into throttle body bracket.

3. Install speed control cable connector onto throttle body bellcrank pin (push rearward to snap into location).

4. Slide throttle (accelerator) cable plastic mount into throttle body bracket. Continue sliding until cable release tab

is aligned to hole in throttle body mounting bracket.

5. While holding throttle to wide open position, place throttle cable pin into throttle body bellcrank.

6. Install air intake tube to top of throttle body.

7. Connect negative battery cable at battery.

8. Before starting engine, operate accelerator pedal to check for any binding.

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SPEED CONTROL

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