GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Corvette 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Radio Poor Reception

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

AM and FM radio reception is dependent on the following components:

    • Radio antennas - left and right - in the rear compartment
    • Coax cables between the radio antennas and the radio antenna modules
    • Radio antenna modules - left and right
    • Coax cables between the radio antenna modules and the radio
    • Radio

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 V over the FM composite signal wire and this switches the modules into FM mode. The left antenna module sends 5-8 V 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.

Diagnostic Aids

Poor AM and FM radio reception is dependent on multiple influences, some of which may not be vehicle related. Areas which have high RF traffic or block the signal path may cause a degradation in radio reception. Radio reception may also be influenced by items within the vehicle, but not part of the radio system. Such examples are aftermarket electrical accessories or other items which may generated noise in the vehicle electrical system.

Reference Information

Schematic Reference

Radio/Navigation System Schematics

Connector End View Reference

Entertainment/Communication Connector End Views

Description and Operation

Radio/Audio System Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Circuit/System Verification

Radio ON, tune to several known FM, AM, and XM (if equipped) stations, and play a known good CD.

⇒If audio output is poor from all sources, refer to Reduced Volume - One or More Speakers.
⇒If both AM and FM reception is poor, refer to Circuit/System Testing.

Circuit/System Testing
  1. Inspect the radio antennas for damage and proper mounting.
    2. ⇒If damage is found, repair or replace as necessary.
  2. Inspect each radio antenna module grounding surface and the mounting hardware for any corrosion that may cause a poor ground.
    3. ⇒If corrosion is noted, clean the grounding surfaces and hardware.
  3. Ignition OFF, disconnect the X2 harness connector at the left radio antenna module. Test for infinite resistance between the terminals listed below and ground.
    4. • Left Antenna Signal -- AM -- terminal 1
    • Left Antenna Signal -- FM -- terminal 2
    ⇒If less than specified value, replace the appropriate antenna.
  4. Ignition OFF, disconnect the X1 harness connector at the right radio antenna module. Test for infinite resistance between the Right Antenna Signal -- FM2 -- terminal 1 and ground.
    5. ⇒If less than specified value, replace the antenna.
  5. Reconnect the X2 harness connector at the left antenna module and the X1 harness connector at the right antenna module.
  6. Ignition OFF, disconnect the X1 harness connector at the left radio antenna module.
  7. Radio ON, test for 10 - 12 V between the Antenna Enable signal circuit terminal 1 and ground.
    8. ⇒If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the radio.
  8. Radio tuned to FM, test for 4.5 - 8.5 V on the FM composite signal circuit terminal 2.
    9. ⇒If less than specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the radio.
    ⇒If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the radio.
  9. Ignition OFF, connect the harness connector at the left antenna module.
  10. Disconnect the coax cable from the right antenna module.
  11. Ignition ON, radio tuned to FM, test for 4.5 - 8.5 V between the center terminal and the outer shield.
    12. ⇒If less than specified range, test the coax for a short to ground. If the circuit tests normal, replace the left antenna module.
    ⇒If greater than the specified range, test the coax for a short to voltage. If the circuit tests normal, replace the left antenna module.

    Note: For steps 14-18, perform the tests on each of the disconnected coax cables.

  12. Ignition OFF, disconnect the coax cables at the radio and radio antenna modules.
  13. Test for infinite resistance between the antenna coax center terminal and ground.
    14. ⇒If less than the specified value, replace the antenna coax.
  14. Test for less than 5Ω on the antenna coax center terminal from end to end.
    15. ⇒If greater than the specified range, replace the antenna coax.
  15. Test for less than 5Ω on the antenna coax outer shield from end to end.
    16. ⇒If greater than the specified range, replace the antenna coax.
  16. Test for infinite resistance between the coax center terminal and the outer shield.
    17. ⇒If less than the specified value, replace the antenna coax.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Radio Antenna Module Replacement
    •  Control Module References for Radio replacement, setup, and programming