Diagnosis And Testing; Antenna Relay; Audio System - Jeep 1997 Grand Cherokee Service Manual

8F - 4 AUDIO SYSTEMS
DESCRIPTION AND OPERATION (Continued)
rent and ground to the proper brushes of the revers-
ible power antenna motor when the ignition switch
and radio switch are turned to the On or Off posi-
tions. See the Diagnosis and Testing section of this
group for more information on the operation of the

antenna relay.

The antenna relay is located in the junction block
on the right cowl side panel, under the instrument
panel in the passenger compartment.
The antenna relay cannot be repaired and, if faulty
or damaged, it must be replaced.
RADIO NOISE SUPPRESSION
Radio Frequency Interference (RFI) and Electro-
Magnetic Interference (EMI) noise suppression is
accomplished primarily through circuitry internal to
the radio receivers. These internal suppression
devices are only serviced as part of the radio receiver.
External suppression devices that are serviced, and
should be checked in the case of RFI or EMI noise
complaints, include the following:
• Radio antenna base ground
• Radio chassis ground wire, strap, or bracket
• Engine-to-body ground strap (if the vehicle is so
equipped)
• Cab-to-bed ground strap (if the vehicle is so
equipped)
• Heater core ground strap (if the vehicle is so
equipped)
• Resistor-type spark plugs
• Radio suppression-type secondary ignition wir-
ing.
In addition, if the source of RFI or EMI noise is
identified as a component on the vehicle (i.e., gener-
ator, blower motor, etc.), the ground path for that
component should be checked. If excessive resistance
is found in that circuit, repair that circuit as
required before considering any component replace-
ment.
If the source of the noise is identified as two-way
mobile radio or telephone equipment, check the
equipment installation for the following:
• Power connections should be made directly to
the battery, and fused as closely to the battery as
possible.
• The antenna should be mounted on the roof or
toward the rear of the vehicle. Remember that mag-
netic antenna mounts on the roof panel can adversely
affect the operation of an overhead console compass,
if the vehicle is so equipped.
• The antenna cable should be fully shielded coax-
ial cable, should be as short as is practical, and
should be routed away from the factory-installed
vehicle wire harnesses whenever possible.
• The antenna and cable must be carefully
matched to ensure a low Standing Wave Ratio
(SWR).
Fleet vehicles are available with an extra-cost RFI-
suppressed Powertrain Control Module (PCM). This
unit reduces interference generated by the PCM on
some radio frequencies used in two-way radio com-
munications. However, this unit will not resolve com-
plaints of RFI in the commercial AM or FM radio
frequency ranges.

DIAGNOSIS AND TESTING

AUDIO SYSTEM

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO
RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING WHEEL,
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY
GROUP 8M - PASSIVE
STEERING COLUMN,
ZG
OR