Poor radio reception
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Cadillac DTS Forum - 2006 through 2012 Discussion, Poor radio reception in Past Cadillac Vehicle Discussion; Hello everybody, I have been experiencing poor radio reception lately, and was wondering if anybody here may be able to ...
  1. #1
    cmcdonald is offline Cadillac Owners Member
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    Poor radio reception

    Hello everybody, I have been experiencing poor radio reception lately, and was wondering if anybody here may be able to help. Some of the weaker FM stations around here seem to fade out a lot, and some days they are just completely static. I have checked the antenna in the rear glass, and the grid appears to be intact, no nicks or missing spots. Also the antenna lead connection to the rear glass is tight, so that is most likely not the issue. I was wondering if there is a powered signal booster somewhere along the antenna lead that may have failed and need replacing? Has anyone else experienced anything like this? These stations had no issues a few months ago, so I am assuming something changed with the car. Thanks for your help.

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  3. #2
    Stepside is offline Cadillac Owners Enthusiast
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    Re: Poor radio reception

    Was any sun protection film installed on the vehicle?

  4. #3
    MrZoSo is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    If you have privacy glass that is the issue...At that point you will need satellite radio.

  5. #4
    cmcdonald is offline Cadillac Owners Member
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    Re: Poor radio reception

    Thanks for the responses. There isn't any tint or films on the window. It is just the regular clean clear factory glass.

  6. #5
    Atavar is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    I don't see how a window film would affect radio reception -- unless you put the film on the *outside* of the glass. You could line the inside of your windows with tin foil and so long as the antenna is outside of the tin foil it should not hurt reception. It might even help.
    In the case of factory limo tint, if it is a metallic tint and is in the glass (outside of the antenna) I could see that possibly affecting reception.

  7. #6
    Eddie39's Avatar
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    Re: Poor radio reception

    Antennas are a tune circuit and any metal close to them can change it. I have tint on my window and it affects my AM signal and I don't have any problems with FM. The antenna in the rear glass works only with AM and it's my understanding the antenna in both glass work with the FM.

    When I brought my car the AM didn't work at all and the dealer had to replace a module up in the rear headliner. I've was told by the dealer that just a bad connection in any of that network will cause signal problems.

  8. #7
    danog is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    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.

    Diversity Antenna System

    This diversity antenna system is comprised of 3 antenna grid patterns interfacing with the rear defog grid, a radio antenna module, a coax, and a 14-volt power feed from the radio to the antenna module.
    In AM and WX mode, the system functions as follows:
    The antenna module takes the signal from only the AM/FM1 antenna pattern on the rear window. The antenna module amplifies this signal and sends it to the radio. In this mode the radio does not supply any voltage to the center conductor of the coax and there is no feedback signal present on the coax.

    In FM mode the system functions as follows:

    The antenna module takes the best signal from 1 of the 3 FM antenna patterns on the rear window. The antenna module amplifies this signal and sends it to the radio. In this mode, the radio supplies 12 volts to the center conductor of the coax and this switches the module into FM mode. The radio also supplies a feedback signal, along the coax, to the AM/FM antenna module, which indicates the quality of the signal. Based on the measured input signal level and the feedback from the radio, the antenna module switches between the 3 antennas to find the best 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 radio antenna module is not grounded properly. The module grounding screws should be clean and tight. The antenna module ground is 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 antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs.
    • Defective antenna module—Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.
    • Defective antenna grid—Refer to Rear Window Replacement.

    Poor Reception on AM Band Only

    • The antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs.
    • Defective antenna module—Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.
    • Defective antenna grid—Refer to Rear Window Replacement.

    Poor Reception on FM Band Only

    • The Antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs.
    • Defective antenna module—Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.
    • Defective antenna grid—Refer to Rear Window Replacement.


    Diversity Antenna System • The AM-FM antenna is integrated with the rear window defogger. Aftermarket glass tinting with metallic film will interfere with or distort the incoming radio reception. If static is heard on the radio with the rear window defogger turned on, it could mean that a defogger grid line has been damaged

  9. #8
    Atavar is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    Quote Originally Posted by danog View Post
    Radio Poor Reception
    In AM and WX mode, the system functions as follows:
    OOh, there's a WX mode? I gotta check that out..

  10. #9
    cmcdonald is offline Cadillac Owners Member
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    Re: Poor radio reception

    Hi everybody, thanks for your responses! So I figured out the problem this afternoon. I decided to pull the radio to check all of the connections. What I found was simply amazing. Someone had spliced a new end on the antenna feed where it plugs into the radio, but they did it by twisting the wires together, and wrapping with electrical tape! So I redid everything using crimp type wire connectors, and the problem is completely solved. Would have been better to solder everything, but I don't have a soldering iron handy, and the crimp connectors seemed to do the trick. For the life of me, I will never understand how people think twisting wires together, and wrapping them with tape makes a proper electrical connection!! Oh well, at least the problem is solved, and it was a free fix. Thanks everybody for all of your help!
    Superjim likes this.

  11. #10
    Eddie39's Avatar
    Eddie39 is offline Cadillac Owners Fanatic
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    Quote Originally Posted by danog
    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.

    Diversity Antenna System

    This diversity antenna system is comprised of 3 antenna grid patterns interfacing with the rear defog grid, a radio antenna module, a coax, and a 14-volt power feed from the radio to the antenna module.
    In AM and WX mode, the system functions as follows:
    The antenna module takes the signal from only the AM/FM1 antenna pattern on the rear window. The antenna module amplifies this signal and sends it to the radio. In this mode the radio does not supply any voltage to the center conductor of the coax and there is no feedback signal present on the coax.

    In FM mode the system functions as follows:

    The antenna module takes the best signal from 1 of the 3 FM antenna patterns on the rear window. The antenna module amplifies this signal and sends it to the radio. In this mode, the radio supplies 12 volts to the center conductor of the coax and this switches the module into FM mode. The radio also supplies a feedback signal, along the coax, to the AM/FM antenna module, which indicates the quality of the signal. Based on the measured input signal level and the feedback from the radio, the antenna module switches between the 3 antennas to find the best 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 radio antenna module is not grounded properly. The module grounding screws should be clean and tight. The antenna module ground is 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 antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs.
    • Defective antenna module—Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.
    • Defective antenna grid—Refer to Rear Window Replacement.

    Poor Reception on AM Band Only

    • The antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs.
    • Defective antenna module—Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.
    • Defective antenna grid—Refer to Rear Window Replacement.

    Poor Reception on FM Band Only

    • The Antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs.
    • Defective antenna module—Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.
    • Defective antenna grid—Refer to Rear Window Replacement.


    • Diversity Antenna System • The AM-FM antenna is integrated with the rear window defogger. Aftermarket glass tinting with metallic film will interfere with or distort the incoming radio reception. If static is heard on the radio with the rear window defogger turned on, it could mean that a defogger grid line has been damaged
    Danog,
    There is an antenna in the upper right corner of the windshield, what part does it play in all of this?

  12. #11
    Atavar is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    Isn't that the security system antenna?

  13. #12
    danog is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    FM antenna

  14. #13
    Atavar is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    Quoting what was quoted earlier in this thread..
    "The antenna module takes the best signal from 1 of the 3 FM antenna patterns on the rear window. "

  15. #14
    Eddie39's Avatar
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    Re: Poor radio reception

    This is straight out of the GM service manual and it states 2 antennas.

    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.

  16. #15
    danog is offline Cadillac Owners Fanatic
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    Re: Poor radio reception

    GM’s update to the document earlier. Both are off GM’s website

    Antenna System

    Important: Radio systems with the antenna(s) in the glass are subject to posssible interference when an aftermarket window tint is applied.

    Diversity Antenna

    The diversity antenna system may use both front and back windows with an integral antenna built between the glass layers of the windshield and as an appliqué to the rear glass. Any damage to the antenna requires replacing the glass. This system is designed to deliver the best radio signal reception possible. Two antennas are used to form a diversity system. The primary antenna is part of the rear window and looks similar to the defogger grid. This antenna receives both AM and FM signals. The secondary antenna is part of the front windshield and receives only FM signals.
    The antenna reception signals are sorted out by the radio antenna module. The radio antenna module is enabled when the radio is turned on. When the AM or FM band is selected on the radio, the antenna module connects the rear window antenna directly to the radio. In addition, when the FM band is selected an enable signal is sent to the antenna module. Superimposed on this enable signal is the strength of the signal being received by the radio tuner. The antenna module switches between the antennas, monitoring the radio signal strength and combines the signals and phase aligns them to create one strong signal

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