GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 DTS 🢒 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 - in the front and rear windows
    • Coax cables between the radio antennas and the radio antenna module
    • Radio antenna module
    • Coax cables between the radio antenna module and the radio
    • Radio

Diversity Antenna System

This diversity antenna system is comprised of 2 antennas, 1 radio antenna module, coax cables, and an FM composite signal from the radio to the left antenna module. In AM mode the system functions as follows: The antenna module takes the signal from the rear AM antenna. The 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 5-8V over the FM composite signal wire and this switches the module into FM mode. The antenna module takes signal from the Front antenna and mix that signal with the signal from the rear antenna. The antenna module amplifies both signals and sends the combined signal to the radio. The FM composite signal also provides a feedback signal to the 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

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 Speakers Inoperative - One or More.
⇒If both AM and FM reception is poor, refer to Circuit/System Testing.

Circuit/System Testing
  1. Inspect the radio antenna branches on the rear glass for damage.
    2. ⇒If damage is found, repair or replace as necessary.
  2. Inspect the 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. Disconnect the front antenna coax cable from the radio antenna module and the antenna.
  4. Test for infinite resistance between the antenna coax center terminal and ground.
    5. ⇒If less than the specified value, replace the antenna coax.
  5. Test for less than 5Ω on the antenna coax center terminal from end to end.
    6. ⇒If greater than the specified range, replace the antenna coax.
  6. Test for less than 5Ω on the antenna coax outer shield from end to end.
    7. ⇒If greater than the specified range, replace the antenna coax.
  7. Test for infinite resistance between the coax center terminal and the outer shield.
    8. ⇒If less than the specified value, replace the antenna coax.
  8. Ignition OFF, disconnect the C1 harness connector at the radio antenna module.
  9. Radio ON, test for B+ between the signal circuit terminal 1 and ground.
    10. ⇒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.
  10. Radio tuned to FM, test for 4.5 - 8.5V on the FM composite signal terminal 2.
    11. ⇒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.
  11. Ignition OFF, reconnect the harness connector at the left antenna module.
  12. Ignition OFF, disconnect the coax cables at the radio and radio antenna module.
  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.
  17. Radio ON, verify the radio reception has improved.
    18. ⇒If there is still poor reception, replace the antenna module.
  18. If all circuits test normal, replace the radio.

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