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
.
Antenna System Test
Important: Always zero out the DMM before taking a resistance
measurement in order to ensure an accurate reading.
- Disconnect the negative battery cable.
- Disconnect the antenna lead-in connector from the radio receiver.
- Measure the resistance from the negative battery cable to the coax outer
conductor connector.
- The resistance measured should be 0.20 ohms or less.
- Test the following when the resistance is greater than 0.20 ohms.
| • | The coaxial cable interconnects for a poor connection or corrosion. |
| • | Test for an open or high resistance from the battery negative cable to
the body. Refer to
Circuit Testing
and
Wiring Repairs
in Wiring Systems. |
- After finding and correcting the condition, operate the system in order
to verify the repair.
Perform the Antenna Checking Procedures after confirming the integrity of the
antenna ground.
Diversity Antenna System
Important: This diversity antenna system is comprised
of 3 antenna grid patterns interfacing with the rear defog grid, 2 radio
antenna modules, a coax, and an FM composite signal from the radio to the passenger
antenna module. In AM and WX mode the system functions as follows:
The
passenger antenna module takes the signal from only the AM/FM1 antenna pattern on
the right side quarter glass window. The passenger antenna module amplifies this signal
and sends it to the radio. In this mode, the driver antenna module sends 8 volts
to power the passenger antenna module via coax.
In FM mode the system functions as follows:
The driver antenna module takes signal from FM antenna pattern on the left side
quarter glass window and sends it to the passenger antenna module where it is mixed
with the signal from the right side rear quarter glass window. The driver antenna
module combines and amplifies both signals and sends it to the radio. In this mode
the radio supplies 5-8 volts over the FM composite signal wire and this
switches the modules into FM mode. The driver antenna module sends 8 volts
to power the passenger antenna module via coax. The FM composite signal also provides
a feedback signal to the passenger antenna module, which indicates the quality of
the 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
in Wiring Systems.
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 modules are not grounded properly. The module grounding
screws should be clean and tight. The antenna module grounds are 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 coax between the driver and passenger antenna modules is open or
shorted to ground or short to B+. Test for 8 volts from the center conductor
of the coax from the passenger antenna module. If the voltage is not within or near
the specified value, test the coax for an open or short for ground or short to B+.
Refer to
Circuit Testing
and
Wiring Repairs
in Wiring Systems. |
| • | The FM composite signal circuit to the radio antenna module is open, shorted
to ground, or shorted to B+. Test the FM composite signal circuit for an open or short
to ground. Refer to
Circuit Testing
and
Wiring Repairs
in Wiring Systems. |
| • | Defective antenna module--Replace the antenna module. Refer to
Control Module References
in Computer/Integrating Systems
for replacement, setup, and programming. |
| • | If no failures were found, replace the radio. Refer to
Control Module References
in Computer/Integrating Systems for replacement,
setup, and programming. |
Poor Reception on AM Band Only
| • | Defective Driver Antenna Module, no 8-volt output--Replace
the driver antenna module. Refer to
Control Module References
in Computer/Integrating Systems for replacement, setup, and programming. |
| • | Defective passenger antenna module--Replace the antenna module. Refer
to
Control Module References
in Computer/Integrating
Systems for replacement, setup, and programming. |
Poor Reception on FM Band Only
| • | Defective driver or passenger antenna module--Replace the antenna
module. Refer to
Control Module References
in Computer/Integrating Systems for replacement, setup, and programming. |
