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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Corvette 🢒 Accessories 🢒 Entertainment 🢒 Radio Poor Reception

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.

  1. Disconnect the negative battery cable.
  2. Disconnect the antenna lead-in connector from the radio receiver.
  3. Measure the resistance from the negative battery cable to the coax outer conductor connector.
  4. The resistance measured should be 0.20 ohms or less.
  5. Test the following when the resistance is greater than 0.20 ohms.
    6. • 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 .
  6. 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

This diversity antenna system is comprised of 3 antennas, 2 radio antenna modules, a coax, and an FM composite signal from the radio to the left antenna module. In AM and WX mode the system functions as follows: The left antenna module takes the signal from the AM antenna. The left antenna module amplifies this signal and sends it to the radio. In FM mode the system functions as follows: In this mode the radio supplies 5-8 volts over the FM composite signal wire and this switches the modules into FM mode. The left antenna module sends 8 volts to power the right antenna module via coax. The right antenna module takes signal from the FM2 antenna and sends it to the left antenna module where it is mixed with the signal from the FM1 antenna. The left antenna module combines and amplifies both signals and sends the combined signal to the radio. The FM composite signal also provides a feedback signal to the left 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 .

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 antenna enable circuit is open or shorted to ground. Test for battery voltage on the antenna enable circuit at the left antenna module. If the voltage is not near the specified value, test the antenna enable circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .
    • 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 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 .
    • Defective left antenna module--Replace the left antenna module. Refer to Radio Antenna Module Replacement for replacement.
    • Defective left antenna--Replace the left antenna. Refer to Circuit Testing and Wiring Repairs .
    • Defective coax between the left antenna module and the radio. Refer to Circuit Testing and Wiring Repairs .
    •  If no failures were found, replace the radio. Refer to Control Module References for replacement, setup, and programming.

Poor Reception on AM Band Only

    • Defective left antenna module--Replace the left antenna module. Refer to Radio Antenna Module Replacement for replacement.
    • Defective AM antenna--Replace the antenna.
    • 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 .

Poor Reception on FM Band Only

    • Defective radio, no 12-volt output at the antenna enable circuit--Replace the radio. Refer to Control Module References .
    • Defective left or right antenna module--Replace the antenna module. Refer to Radio Antenna Module Replacement .
    • Defective FM1 or FM2 antenna--Replace the antenna.
    • Defective coax between the left and right antenna modules--Refer to Circuit Testing and Wiring Repairs .
    • 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 at the left antenna module for 5-8 volts. If the voltage is not within or near the specified value, test the FM composite signal circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .
    • The coax between the left and right 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 left antenna module. If the voltage is not within or near the specified value, test the coax for an open or short to ground or short to B+. Refer to Circuit Testing and Wiring Repairs .