Jeep 1997 Grand Cherokee Service Manual page 463

ZG
DIAGNOSIS AND TESTING (Continued)
SPEED CONTROL ELECTRICAL TEST
Two different test methods may be used to check
the electronic speed control system. One involves
using the DRB scan tool. If this test method is
desired, refer to the appropriate Powertrain Diagnos-
tic Procedures service manual.
The other test method will involve the use of a
volt/ohm meter. The volt/ohm meter method is
described within the tests on the following pages.
Refer to Group 8W, Wiring Diagrams for speed con-
trol electrical schematics and connector location.
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, should be applied.
Inspect connectors for damaged terminals. A poor
electrical connection can cause a complete or inter-
mittent malfunction. For this reason, a poor connec-
tion may be misdiagnosed
malfunction.
VEHICLE SPEED SENSOR
For diagnosis and testing of the Vehicle Speed Sen-
sor (VSS), refer to the appropriate Powertrain Diag-
nostic Procedures service manual. Also refer to the
DRB scan tool.
SPEED CONTROL SWITCHES
For complete speed control system diagnosis, refer
to the appropriate Powertrain Diagnostic Procedures
manual. To test each of the speed control switches
only, refer to the following:
WARNING: BEFORE ATTEMPTING TO DIAGNOSE,
REMOVE OR INSTALL ANY AIRBAG SYSTEM OR
RELATED STEERING WHEEL AND STEERING COL-
UMN COMPONENTS, YOU MUST FIRST DISCON-
NECT AND ISOLATE THE BATTERY NEGATIVE
(GROUND) CABLE. WAIT 2 MINUTES FOR SYSTEM
CAPACITOR TO DISCHARGE BEFORE FURTHER
SYSTEM SERVICE. FAILURE TO DO SO COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.
(1) Disconnect negative battery cable. Wait 2 min-
utes for airbag system capacitor to discharge.
(2) Remove the two speed control switch modules
from steering wheel. Refer to the removal/installation
section for procedures.
as a component
SWITCH
VEHICLE SPEED CONTROL SYSTEM
(3) Check continuity of each individual speed con-
trol switch module as shown in chart (Fig. 1). If OK,
reinstall switch. If not OK, replace switch module
assembly.
Fig. 1 Speed Control Switch Continuity
STOP LAMP SWITCH
For continuity checks and switch adjustment, refer
to Group 5, Brakes.
VACUUM SUPPLY TEST
(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 reservoir. Disconnect vacuum line at res-
ervoir and connect a hand-operated vacuum pump to
reservoir fitting. Reservoir vacuum should not bleed
off. If vacuum is being lost, replace reservoir.
SPEED CONTROL SERVO
For complete speed control system diagnosis, refer
to the appropriate Powertrain Diagnostic Procedures
manual. To test the speed control servo only, refer to
the following:
8H - 5