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
Tools Required
J 39916-A CD and Cassette
Diagnostic Audio Kit
| | 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.
|
| • | Inspect for any aftermarket equipment that may have been installed on the vehicle.
If aftermarket equipment is found, disconnect the equipment and verify that the audio
noise is still present. |
| | Verify 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, inspect for the following items
before speaker replacement: |
| - | Inspect for a loose or incorrectly installed speaker or surrounding trim.
Loose trim may 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. |
| • | Verify 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, in order
to ensure that they are clean and tight. |
| • | Compare the customers vehicle to another of similar model and audio system
in order to determine if the condition is abnormal. |
Identifying Concerns
- In order to isolate the source of the noise/poor reception, identify the
ignition switch position that the concern is most noticeable:
| 1.1. | Turn the ignition switch to the accessory position. |
| 1.3. | Seek up 88 to 108 FM then 550 to 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 repeat
the steps again with the engine running. |
- Return the ignition switch to the position that the concern was most noticeable.
- Remove the fuses or circuit breakers, one at a time, until the noise has
been eliminated.
- Identify what systems or components are powered by the fuse.
- Reinstall all fuses and circuit breakers.
- 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. Try
variations of the following repairs: |
| • | Try adding 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 volt) capacitor GM P/N 1227895 |
| - | This works well for ignition system related noise. |
| - | 0.47 micro farad capacitor GM P/N 1227894 |
| - | This works well for switches and relays. |
| - | Feed through capacitor GM P/N 477371 |
| - | This works
well for high current situations. |
| - | Filter package GM P/N 1224205 |
| - | This works well
for low current situations. |
| - | Fuel pump suppressor GM P/N 25027405 |
| - | 21 inch braided ground strap GM P/N 8910791 |
| - | 19 inch braided ground strap GM P/N 6286800 |
| - | 10.5 inch braided ground strap GM P/N 6287160 |
| - | 8.5 inch braided ground strap GM P/N 12091511 |
Generator Whine Concerns
- Inspect the ground terminal and cable for high resistance.
- Inspect the generator and brackets for loose or coated mounting bolts.
- Verify that the ground straps between the engine and the frame are clean
and tight.
- If the noise is still present, inspect the charging system for proper
operation. Refer to
Diagnostic System Check - Engine Electrical
in Engine Electrical.
- Install a filter GM P/N 1224205 in the battery voltage feed
circuit to the radio.
- If the noise is not eliminated, install the filter in each following variation:
| • | 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 that the two-wire side is toward the radio with
the ground wire attached to chassis ground. |
| • | Remove the ground from the filter. |
- 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.
- Before reassembling the vehicle, remove any unneeded filters.
- Test the functionality of all the vehicle systems, including those not
related to the audio system, for proper operation and function.
