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Radio Poor Reception




Radio Poor Reception

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions 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 antenna
* Coax cable between the radio antenna and the radio antenna module
* Radio antenna module
* Coax cable between the radio antenna module and the radio
* Radio

Diagnostic Aids

Note: Radio systems with the antenna(s) in the glass are subject to possible interference when an aftermarket window tint is applied, especially when there is a metallic present in the film.

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 generate noise in the vehicle electrical system.

AM reception is highly dependent on the antenna module receiving battery voltage from the radio and being properly grounded. The antenna module has a built in antenna amplifier that boosts both AM and FM reception. When the antenna module does not receive power, AM stations will not be received and FM reception will be limited. If the module is not properly grounded, excessive interference in the signal may occur, or reception may be limited.

Reference Information
Schematic Reference

Radio/Navigation System Schematics Radio/Navigation System Schematics
Connector End View Reference

Component Connector End Views Connector Views
Description and Operation

Radio/Audio System Description and Operation Radio/Audio System
Electrical Information Reference

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

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Inspect the antenna for proper mounting or physical damage.

• If damage is found, repair or replace as necessary

2. 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 Speaker Malfunction Speaker Malfunction.

Circuit/System Testing

Rear Glass Antenna Testing
1. Inspect the antenna on the rear glass. Verify all branches of the antenna are intact, with no scratches or other damage.

• If damage is found, repair or replace as necessary.

2. Verify the connector at the back glass is properly secured and free of any damage.

• If damage is found, repair or replace as necessary.

3. Inspect the radio antenna module grounding surfaces and the mounting hardware for any corrosion that may cause a poor ground.

• If corrosion is noted, clean the grounding surfaces or hardware.

4. Ignition OFF, disconnect the harness connector at the radio antenna module.
5. Ignition ON, radio ON, test for B+ between the signal circuit terminal 1 and ground.

• 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.

6. Disconnect the antenna coax from the radio and the radio antenna module.
7. Test for infinite resistance between the antenna coax center terminal and ground.

• If less than the specified value, replace the antenna coax.

8. Test for infinite resistance between the coax center terminal and the outer shield.

• If less than the specified value, replace the antenna coax.

9. Test for less than 5 Ohms on the antenna coax center terminal from end to end.

• If greater than the specified value, replace the antenna coax.

10. Test for less than 5 Ohms on the antenna coax outer shield from end to end.

• If greater than the specified value, replace the antenna coax.

11. If all circuits test normal, replace the antenna module. Reconnect the antenna coax.
12. Ignition ON, radio ON, verify radio reception has improved.

• If reception is still poor, replace the radio.

Fixed Mast Antenna Testing
1. Ignition OFF, disconnect the radio antenna coax cable from the radio and the radio antenna.
2. Test for infinite resistance between the antenna coax center terminal and ground.

• If less than the specified value, replace the antenna coax.

3. Test for infinite resistance between the coax center terminal and the outer shield.

• If less than the specified value, replace the antenna coax.

4. Test for less than 5 ohm on the antenna coax center terminal from end to end.

• If greater than the specified range, replace the antenna coax.

5. Test for less than 5 ohm on the antenna coax outer shield from end to end.

• If greater than the specified range, replace the antenna coax.

6. Reconnect the coax to the radio antenna. Test for infinite resistance on the coax at the radio between the center terminal and the outer shield.

• If less then specified value, replace the antenna.

7. Test for less than 10 ohm on the coax at the radio between the outer shield and ground.

• If greater than specified value, clean the mounting surface of the antenna ground plane. If no corrosion found, replace the antenna.

8. If all circuits test normal, replace the radio.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Radio Antenna Module Replacement (9R199537 and Earlier) Radio Antenna Module Replacement (9R199537 and Earlier)Radio Antenna Module Replacement (9R199538 and Later) Radio Antenna Module Replacement (9R199538 and Later)
* Antenna Cable Replacement (W/O Fixed Antenna) Antenna Cable Replacement (W/O Fixed Antenna)
* Radio Antenna Cable Extension Cable Replacement (Avalanche/Escalade EXT)
* Radio Antenna Replacement Radio Antenna Replacement
* Control Module References Control Module References for radio replacement, setup, and programming

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