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: |
| • | 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
- In order to isolate the source of
the noise/poor reception, identify the ignition switch position that the concern
is most noticeable:
| • | Turn the ignition switch to the
accessory position. |
| • | Seek up 88 to 108 FM then 550 to 1600 AM. |
| • | Record the number of valid radio stations where
the tuner stops. |
| • | Repeat these steps with the ignition
ON, and the engine OFF then again with the engine running. |
- Return the ignition switch to the position that the concern was
most noticeable.
- Remove 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° 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 - 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 |
| - | 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.
- Inspect 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 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 all of the vehicle systems (including those not
related to the audio system) for proper operation and function.
