Schematic Reference:
Radio/Audio System Schematics
Diagnostic System Check - Vehicle
Always perform the Diagnostic System Check - Vehicle, before proceeding
with these diagnostic procedures. Refer to
Diagnostic System Check - Vehicle.
Diversity Antenna System
This diversity antenna system is comprised of 3 antenna grid patterns
interfacing with the rear defog grid, a radio antenna module, a coax, and a 14-volt
power feed from the radio to the antenna module.
In AM and WX mode, the system functions as follows:
The antenna module takes the signal from only the AM/FM1 antenna pattern on
the rear window. The antenna module amplifies this signal and sends it to the radio.
In this mode the radio does not supply any voltage to the center conductor of the
coax and there is no feedback signal present on the coax.
In FM mode the system functions as follows:
The antenna module takes the best signal from 1 of the 3 FM antenna patterns
on the rear window. The antenna module amplifies this signal and sends it to the radio.
In this mode, the radio supplies 12 volts to the center conductor of the coax
and this switches the module into FM mode. The radio also supplies a feedback signal,
along the coax, to the AM/FM antenna module, which indicates the quality of the signal.
Based on the measured input signal level and the feedback from the radio, the antenna
module switches between the 3 antennas to find the best signal.
The following information lists the most probable cause of the concern to the
least probable cause, followed by the appropriate test for that condition. If the
test leads to the replacement of a component, always inspect for a poor connection
before proceeding with the replacement. Refer to
Testing for Intermittent Conditions and Poor Connections and
Connector Repairs.
Perform the Antenna System Test and test the antenna coax cable prior to performing
any of the following tests.
Poor Reception on Both AM and FM Bands
| • | The radio antenna module is not grounded properly. The module grounding
screws should be clean and tight. The antenna module ground is either a chassis ground
or a ground strap. Measure the resistance from the antenna module base plate to a
good ground. Resistance should be 0.20 ohms or less. Find and correct the condition
if the resistance is out of specification. |
| • | The antenna 14-volt switch supply voltage circuit to the radio antenna
module is open or shorted to ground. Test the antenna 14-volt switch supply voltage
circuit for an open or short to ground. Refer to
Circuit Testing and
Wiring Repairs. |
Poor Reception on AM Band Only
| • | The antenna 14-volt switch supply voltage circuit to the radio antenna
module is open or shorted to ground. Test the antenna 14-volt switch supply voltage
circuit for an open or short to ground. Refer to
Circuit Testing and
Wiring Repairs. |
Poor Reception on FM Band Only
| • | The Antenna 14-volt switch supply voltage circuit to the radio antenna
module is open or shorted to ground. Test the antenna 14-volt switch supply voltage
circuit for an open or short to ground. Refer to
Circuit Testing and
Wiring Repairs. |
