GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1999 🢒 S/T Isuzu - 2WD 🢒 Body and Accessories 🢒 Entertainment 🢒 Audio Preliminary Diagnosis

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. Before attempting to diagnose any audio system problems, ensure that you fully charge the battery.

If the voltage is below 9 volts, incorrect diagnosis may result.

Troubleshooting Hints

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

    • 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 thay are attempting to receive.
    • Compare the customers vehicle to another of similar model and audio system to determine if the condition is abnormal.
    • Most normal audio noises can be found on weak stations near the low end of the band. This noise is considered to be a normal condition.
    • 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.
    • If the noise is only from one speaker check for the flowing before speaker replacement:
      • Check that the speaker connections are clean and tight.
      • Check that the speaker mounting is tight.
      • Inspect for loose or incorrectly installed speaker or surrounding trim.
    • Ignition noise on the FM band may be a indicator of a ignition system breakdown.
    • Inspect that all vehicle grounds are clean, tight and free of corrosion.
    • Inspect the rear defogger grid lines for breaks or dark spots.
    • Inspect the connections at the radio antenna module and ground coil to ensure that they are clean and tight.

Identifying Concerns

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

  1. To help isolate the source of the noise, identify the ignition switch position that the noise is most noticeable:
    2. • Turn the ignition switch to the accessory position and listen for the noise.
    • Turn the ignition switch to the run position with the engine off.
    • Turn the ignition switch to the run position with the engine running.
  2. Turn the ignition switch to the position that the noise was most noticeable.
  3. Remove the vehicle fuses and 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 power by the fuse one at a time until the noise 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 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. Try varying the following techniques:
       - Try just adding the tape before adding a ground strap to the tape.
       - Wrap a ground strap 360° around the tape, securing the other end of the strap to chassis ground.
       - Add a ground strap to both ends of the tape.

       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 induced from a switch operation, perform one or more of the following capacitor applications, 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 mF (50V) capacitor
       - 0.47 mF capacitor
       - Fuse block capacitor
       - Feed through capacitor
       - Filter package
       - Turn signal suppression
       - Fuel pump suppressor
       - 21 in. braided ground strap
       - 19 in. braided ground strap
       - 10.5 in. braided ground strap
       - 8.5 in. braided ground strap

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 go to Charging System Check
  5. Install a filter in the battery voltage feed circuit to the radio.
  6. If the noise is not eliminated, install the filter in the following variations:
    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 two-wire side is toward the radio with the ground wire attached to chassis ground.
    • Remove the ground from the filter.
  7. Install a filter in the ignition voltage feed to the radio.
  8. If the noise is not eliminated, install the filter in the following variations:
    9. • 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 two-wire side is toward the radio with the ground wire attached to chassis ground.
    • Remove the ground from the filter.
  9. If the filter causes delays in the radio when turning ON or OFF, or other problems, remove the filter and Install a 0.47 mF capacitor to chassis ground.
  10. Before reassembling the vehicle, remove any unneeded filters.
  11. Inspect all of the vehicle systems (including those not related to the audio system) for proper operation and function.