GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 CTS 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Audio System Troubleshooting Hints

Tools Required

J 39916-A CD and Cassette Diagnostic Audio Kit

Many conditions that affect radio operation may be corrected without removing the radio from the car. Verify the condition, and follow the diagnostic procedures in order to isolate and correct the condition. In order to properly diagnose any audio system problems, ensure that you have a fully charged battery.

Preliminary Inspections

       Important: When testing the audio system for poor reception or noise, the vehicle should be outside away from metal buildings and utility lines, with the hood and rear compartment closed.

    • Check for any aftermarket equipment that may have been installed on the vehicle. If aftermarket equipment is found disconnect it and check if the audio noise is still present.
        Inspect that the antenna connector and the antenna coaxial cable are clean and tight.
    • For reception concerns, first determine if the customer is within the listening area of the stations they are attempting to receive.
    • Stations at the lower end of the FM band are more susceptible to audio noises than stations at the higher end.
    • If the noise is only from one speaker check for the following before speaker replacement:
       - Isolate the noise using the J 39916-A .
       - Inspect the speaker connections to ensure they are clean and tight. Refer to Testing for Intermittent Conditions and Poor Connections .
       - Inspect for a loose or incorrectly installed speaker or surrounding trim. Loose trim can cause a buzz or flutter which sounds like a malfunctioning speaker.
    • Ignition noise on the FM band may be an indication of an ignition system problem.
    • Inspect that all vehicle grounds are clean, tight and free of corrosion.
    • Inspect the rear defogger grid lines for large breaks or dark spots.
    • Inspect the connections at the radio antenna module (if equipped) to ensure that they are clean and tight.
    • Compare the customers vehicle to another of similar model and audio system to determine if the condition is abnormal.

Identifying Concerns
  1. In order to isolate the source of the noise/poor reception, identify the ignition switch position that the concern is most noticeable:
    2. 1.1. Turn the ignition switch to the accessory position.
    1.2. Turn ON the radio.
    1.3. Seek up 88-108 FM then 550-1600 AM.
    1.4. Record the number of valid radio stations where the tuner stops.
    1.5. Repeat these steps with the ignition ON, and the engine OFF then again with the engine running.
  2. Return the ignition switch to the position that the concern was most noticeable.
  3. Remove fuses or circuit breakers one at a time until the noise has been eliminated.
  4. Identify what systems or components are powered by the fuse.
  5. Reinstall all fuses and circuit breakers.
  6. Disconnect the components powered by the fuse one at a time until the concern has been eliminated.

Corrective Action
    • Inspect the ground integrity of the component or system causing the noise.
    • Malfunctioning and marginal components such as relays and solenoids may cause noise and/or poor reception.
    • Always use a braided ground strap when applying additional grounds and keep the ground strap as short as possible.
    • If the noise source is found to be coming from the vehicle harness:
       - Route the antenna cable separately from the wire harness that is emitting the noise.
       - Use aluminum or nickel tape in order to shield the antenna cable. Attempt variations of the following repairs:
   • Add only aluminum or nickel tape before adding a ground strap to the tape.
   • Wrap a ground strap 360 degrees around the tape, securing the other end of the strap to chassis ground.

       Important: When installing suppression devices, signal wires such as sensor and communication circuits should not be suppressed. Battery and ignition voltage circuits are the best choices for suppressing.

    • Capacitors work best on switch pops and low frequency noise.
    • Filters work best on high frequency whines and static.
    • After adding any suppression device, inspect all of the vehicle systems (including those not related to the audio system) for proper operation and function.
    • Whenever possible, make a test harness that includes filters or capacitors. Always inspect the effectiveness and operation before permanent installation.
    • If an audible pop is caused due to operating a switch, perform the following repairs as necessary:
       - Add a capacitor across the contacts of the switch.
       - Add a capacitor from the battery positive voltage (B+) side of the switch to chassis ground.
       - Add a capacitor from the ground side of the switch to chassis ground.
    • Use the following available noise suppression devices:
       - 220 micro farad (50 V) capacitor GM P/N 1227895--Works well for ignition system related noise.
       - 0.47 micro farad capacitor GM P/N 1227894--Works well for switches and relays.
       - Feed through capacitor GM P/N 477371--Works well for high current situations.
       - Filter package GM P/N 1224205--Works well for low current situations.
       - Fuel pump suppressor GM P/N 25027405
       - 53.34 cm (21 in) braided ground strap GM P/N 8910791
       - 48.26 cm (19 in) braided ground strap GM P/N 6286800
       - 26.67 cm (10.5 in) braided ground strap GM P/N 6287160
       - 21.59 cm (8.5 in) braided ground strap GM P/N 12091511

Generator Whine Concerns
  1. Inspect the ground terminal and cable for high resistance.
  2. Inspect the generator and brackets for loose or coated mounting bolts.
  3. Inspect that the ground straps between the engine and the frame are clean and tight.
  4. If the noise is still present, inspect the charging system for proper operation.
  5. Install a filter GM P/N 1224205 in the battery voltage feed circuit to the radio.
  6. If the noise is not eliminated, install the filter in each following variation:
    7. • Install the filter with the single wire side toward the radio and the ground wire attached to chassis ground.
    • Remove the ground to the filter.
    • Reverse the filter so the 2-wire side is toward the radio with the ground wire attached to chassis ground.
    • Remove the ground from the filter.
  7. If the filter GM P/N 1224205 causes a delay when turning the radio ON or OFF, or other problems, remove the filter and install a 0.47 micro farad capacitor to chassis ground.
  8. Before reassembling the vehicle, remove any unneeded filters.
  9. Test the functionality all of the vehicle systems (including those not related to the audio system) for proper operation and function.