Stop Lamp Switch; Vacuum Reservoir; Vehicle Speed Sensor; Diagnosis And Testing - Chrysler neon 1997 Service Manual

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DESCRIPTION AND OPERATION (Continued)
existing recorded target speed, depress and hold the
SET/COAST switch until the desired speed is
reached. Then release the switch. The ON and OFF
switches operates two
ON/OFF input, and the battery voltage to the brake
switch, which powers the speed control servo.
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 in the same location as the conventional
stop lamp switch, on the brake pedal mounting
bracket under the instrument panel. The PCM mon-
itors the state of the dual function stop lamp switch.
Refer to Group 5, Brakes for more information on
stop lamp switch service 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.

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.

VEHICLE SPEED SENSOR

The Vehicle Speed Sensor (VSS) is a pulse genera-
tor mounted to an adapter near the transmission out-
put shaft. The sensor is driven through the adapter
by a speedometer pinion gear. The VSS pulse signal
components: the PCM's
VEHICLE SPEED CONTROL SYSTEM
to the speedometer/odometer is monitored by the
PCM speed control circuitry to determine vehicle
speed and to maintain speed control set speed. Refer
to the appropriate Powertrain Diagnostic Procedures
manual for diagnosis and testing of this component.
Refer to Group 14, Fuel System for removal/installa-
tion procedures.

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.
If a road test verifies an inoperative system, and
the speedometer operates properly, check for:
• A Diagnostic Trouble Code (DTC). If a flash
lamp code 15, 34 or 77 exists at the Check Engine
Lamp (MIL), conduct tests per the Powertrain Diag-
nostic 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.
• Loose or leaking vacuum hoses or connections.
• Secure attachment at both ends of the speed
control servo cable.
• Smooth operation of throttle linkage and throttle
body air valve.
• 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.

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 (Fig. 4). The connector
is located at left side of the steering column, and at
lower edge of the panel.
8H - 3