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.
|
| • | 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 (50V) 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 in braided ground strap GM P/N 8910791 |
| - | 19 in braided ground strap GM P/N 6286800 |
| - | 10.5 in braided ground strap GM P/N 6287160 |
| - | 8.5 in 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 electrical 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.
