Chrysler New Yorker. Manual — part 76

When speed control is selected by depressing the

ON switch, the PCM allows a set speed to be stored
in RAM for speed control. To store a set speed,
depress the SET switch while the vehicle is moving
at a speed between 30 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.

NOTE: Depressing the OFF switch or turning off
the ignition switch will erase the set speed stored
in the PCM.

For added safety, the speed control system is pro-

grammed to disengaged for any of the following con-
ditions:

• An indication of Park or Neutral

• A rapid increase rpm (indicates that the clutch

has been disengaged)

• Excessive engine rpm (indicates that the trans-

mission may be in a low gear)

• The speed signal increases at a rate of 10 mph

per second (indicates that the co-efficient 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 RESUME switch when speed is
greater than 25 mph restores the vehicle to the tar-
get speed that was stored in the PCM.

While the speed control is engaged, the driver can

increase the vehicle speed by depressing the ACCEL
switch. The new target speed is stored in the PCM
when the ACCEL is released. The PCM also has a
9tap-up9 feature in which vehicle speed increases at a
rate of approximately 2 mph for each momentary
switch activation of the ACCEL switch. The PCM
also provides a means to decelerate without disen-
gaging speed control. To decelerate from an existing
recorded target speed, depress and hold the COAST
switch until the desired speed is reached, then
release the switch.

The individual switches cannot be repaired. If one

switch fails, the entire switch module must be
replaced.

STOP LAMP SWITCH

Vehicles equipped with the speed control option use

a dual function stop lamp switch. The switch is
mounted on the brake pedal mounting bracket under
the instrument panel. The PCM monitors the state of
the dual function stop lamp switch. Refer to Group 5,

Brakes for more information on stop lamp switch ser-
vice and adjustment procedures.

SERVO CABLE

The speed control servo cable is connected between

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

POWERTRAIN CONTROL MODULE

The speed control electronic control circuitry is

integrated

into

the

Powertrain

Control

Module

(PCM). The PCM is located in the engine compart-
ment. The PCM speed control functions are moni-
tored by the On-Board Diagnostics (OBD). All OBD-
sensed systems are monitored by the PCM. Each
monitored circuit is assigned a Diagnostic Trouble
Code (DTC). The PCM will store a DTC in electronic
memory for any failure it detects. See On-Board
Diagnostic Tests in this group for more information.
The PCM cannot be repaired and must be replaced if
faulty.

USE THE DRB SCAN TOOL TO REPROGRAM

THE NEW PCM WITH THE VEHICLE’S ORIGI-
NAL IDENTIFICATION NUMBER (VIN) AND
THE ORGINAL VEHICLE’S MILEAGE. IF THIS
STEP IS NOT DONE A DIAGNOSTIC TROUBLE
CODE (DTC) MAY BE SET.

VACUUM RESERVOIR

The reservoir contains a one-way check valve to

trap engine vacuum in the reservoir. When engine
vacuum drops, as in climbing a grade while driving,
the reservoir supplies the vacuum needed to main-
tain proper speed control operation. The vacuum res-
ervoir cannot be repaired and must be replaced if
faulty.

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. Speed-
ometer operation should be smooth and without flut-
ter at all speeds.

Flutter in the speedometer indicates a problem

which might cause surging in the speed control sys-
tem. The cause of any speedometer problems should
be corrected before proceeding. Refer to Group 8E,
Instrument Panel and Gauges for speedometer diag-
nosis.

8H - 2

VEHICLE SPEED CONTROL SYSTEM

300M

DESCRIPTION AND OPERATION (Continued)

If a road test verifies a surge following a set and

the speedometer operates properly see “Overshoot/
Undershoot on speed control set”.

If a road test verifies an inoperative system, 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 or corroded electrical connections at the

servo. Corrosion should be removed from electrical
terminals and a light coating of Mopar Multipurpose
Grease, or equivalent, applied.

• Leaking vacuum reservoir.

• Loose or leaking vacuum hoses or connections.

• Defective one-way vacuum check valve.

• Secure attachment at both ends of the speed

control servo cable.

• Smooth operation of throttle linkage and throttle

body air valve.

• Conduct electrical test at PCM.

• Failed 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.

OVERSHOOT/UNDERSHOOT FOLLOWING SPEED
CONTROL SET

If the operator repeatedly presses and releases the

set button with their foot off of the accelerator (a “lift
foot set” to begin speed control operation), the vehicle
may accelerate and exceed the desired set speed by
up to 5 MPH (8 km/h) and then decelerate to less
than the desired set speed before finally achieving
the desired set speed.

The Speed Control has an adaptive strategy that

compensates for vehicle-to-vehicle variations in speed
control cable lengths. When the speed control is set
with the vehicle operators foot off of the accelerator
pedal, the speed control thinks there is excessive
speed control cable slack and adapts. If the lift foot
sets are continually used, the speed control over-
shoot/undershoot condition will develop.

To “unlearn” the overshoot/undershoot condition,

the vehicle operator has to press and release the set
button while maintaining the desired set speed with
the accelerator pedal (not decelerating or accelerat-
ing), and then turn the cruise control switch to the
OFF position (or press the CANCEL button if
equipped) after waiting 10 seconds. This procedure
must be performed approximately 10–15 times to

completely unlearn the overshoot/undershoot condi-
tion.

CHECKING FOR DIAGNOSTIC CODES

When trying to verify a speed control system elec-

tronic malfunction: Connect a DRB scan tool if avail-
able to the data link connector. The connector is
located below the steering column, and at lower edge
of the panel (Fig. 2).

(1) A speed control malfunction may occur without

a diagnostic code being indicated.

Refer to Group 25, for further information and

usage of the DRB scan tool and a more complete list
of Diagnostic Trouble Code.

SPEED CONTROL SLOWS DOWN BY ITSELF

Test vehicle speed sensor, refer to group 8E. If sen-

sor fails replace sensor, if it passes perform the fol-
lowing test:

(1) Perform the speed control switch test (in the

Powertrain

Diagnostic

Manual)

on

the

DECEL

switch, if it fails replace switch.

(2) If the switch passes, conduct the vacuum sup-

ply test.

(3) If it passes, conduct the servo vacuum test. If it

fails replace servo.

(4) If servo passes, replace the PCM.

SPEED CONTROL ELECTRICAL TEST

Electronic speed control systems may be tested

using two different methods. One involves use of a
DRB. If this test method is desired, refer to the Pow-
ertrain Diagnostic Test Procedures for charging and
speed control system manual.

Fig. 2 Data Link Connector

300M

VEHICLE SPEED CONTROL SYSTEM

8H - 3

DIAGNOSIS AND TESTING (Continued)

The other test method uses a volt/ohm meter. The

volt/ohm meter method is described in the following
tests.

If any information is needed concerning wiring,

refer to Group 8W, Wiring Diagrams (Fig. 3).

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.

When electrical connections are removed, corrosion

should be removed from electrical terminals and a
light coating of Mopar Multi-Purpose Grease, or
equivalent, applied. Inspect connectors for damage
terminals.

A poor connection can cause a complete or inter-

mittent malfunction and is also the only connection
in the circuit, that can not be tested. For this reason,
a loose connection may be misdiagnosed as a compo-
nent malfunction.

SPEED CONTROL DIAGNOSTIC TROUBLE CODES

Hex Code

DRB Scan Tool Display

Description of Diagnostic Trouble Code

23

No Vehicle Speed Sensor Signal

No vehicle distance (speed) sensor signal detected

during road load conditions.

OF

Speed Control Solenoid Circuits

An open or shorted condition detected in the

Speed Control vacuum or vent solenoid circuits.

56

MUX S/C Switch High

Speed Control switch input above the maximum

acceptable voltage.

57

MUX S/C Switch Low

Speed Control switch input below the minimum

acceptable voltage.

52

S/C Power Relay Or 12V Driver Circuit

Malfunction detected with power feed to speed

control servo solnoids.

Check Engine Lamp will illuminate during engine operation if this Diagnostic Trouble Code was recorded.

8H - 4

VEHICLE SPEED CONTROL SYSTEM

300M

DIAGNOSIS AND TESTING (Continued)

Fig. 3 Speed Control Circuit

300M

VEHICLE SPEED CONTROL SYSTEM

8H - 5

DIAGNOSIS AND TESTING (Continued)