Audio System Diagnostic Overview
- Verify the customer complaint.
- Follow the radio service procedures.
- If you call for technical assistance, assemble all of the pertinent
information before you place the phone call.
Identifying Concerns
| • | Refer to any technical service bulletins or the Dealer Communication
System. The Dealer Communication System will provide any applicable Preliminary
Information (P/I) for customer concerns. |
| • | Determine if any DTCs are stored. Refer to Engine Controls. |
| • | If the reception is poor, determine if the station is within the
customer's listening area. |
| • | Before you test for audio reception or noise, position the vehicle
outside of the building with the hood closed. |
| • | Duplicate the customer's complaint before you begin to diagnose
the system: |
| - | Ask the customer to demonstrate the condition. |
| - | Test drive the vehicle with the customer. |
| - | Test drive another vehicle that is a similar model with a similar
audio system. |
| • | Before you begin diagnosis, identify which components are involved
and the features of these components. |
| • | Determine if any aftermarket equipment has been installed on the
vehicle. Complete the following steps if aftermarket equipment is present: |
| 1. | Disconnect the aftermarket equipment. |
| 2. | Determine if the customer's complaint still exists. |
| 3. | Reinstall the equipment as needed. Refer to GM guidelines for
the installation of the aftermarket components. |
| • | Complete the following steps in order to identify a faulty component: |
| 1. | Place the ignition into the following positions. Determine in
which position the noise is audible: |
| • | The ON position, with the engine off |
| • | The ON position, with the engine running |
| 2. | Remove the fuses one at a time until the condition is gone. |
| 3. | Mark the fuse or fuses that cause the condition. |
| 4. | Reinstall all of the fuses and the circuit breakers. |
| 6. | Disconnect each of the components that is powered by the complaint
fuse or fuses. |
Disconnect the components one at a time.
| 7. | When the condition is gone, identify the noisy component. |
| 8. | Inspect the ground integrity of the component that is causing
the condition. |
| • | An interference condition may not be an audible noise. |
| • | Most noises can be heard on weak stations near the end of the
band. These noises are normal. |
| • | An ignition noise on FM may indicate that the ignition system
is flawed. |
| • | Malfunction in the following items may cause noise or poor reception: |
Corrective Action
| • | Use the correct tools for diagnosis and repairs. |
| • | The following noise suppression devices are available: |
| - | 220 mF (50 V) capacitor GM P/N 1227895 |
| - | A 0.47 mF capacitor GM P/N 1227894 |
| - | Fuse block capacitor GM P/N 469328 |
| - | Feed through capacitor GM P/N 477371 |
| - | Filter package GM P/N 1224205 |
| - | Turn signal suppression GM P/N 3861565 |
| - | Fuel pump suppressor GM P/N 25027405 |
| - | 53.3 cm (21 in) braided ground strap GM P/N 8910791 |
| - | 48.3 cm (19 in) braided ground strap GM P/N 6286800 |
| - | 26.7 cm (10.5 in) braided ground strap GM P/N 6287160 |
| - | 21.6 cm (8.5 in) braided ground strap GM P/N 12091511 |
| • | Use the Audio Diagnostic Kit GM P/N J 39916-A
to assist in optimizing diagnosis. |
| • | If the condition requires you to send the radio to the service
center, describe the symptoms accurately on the warranty form. Send a copy
of the Service Writer Check List along with the warranty form. |
| • | Take the following precautions in order to prevent damage to CDs
and cassettes: |
| - | Do not leave CDs or cassettes in the car. Extreme heat may cause
permanent damage to CDs and cassettes. |
| - | Store cassettes in their cases. The vibration in the vehicle may
cause the tape to unwind inside of the cartridge. |
| • | Complete the following steps before you remove the speakers: |
| - | Inspect all of the connectors and wiring to the speakers. |
| - | Examine the connectors for bent or loose pins. |
| | Important:
| • | Inspect the antenna coax connectors for the following conditions: |
| • | Route the coax separately from the other wires. |
| • | Shield the antenna coax interconnections with aluminum or nickel
tape. |
| • | Inspect all of the vehicle grounds. Refer to Troubleshooting Procedures
in Cell 4. |
|
| • | If you use a test antenna in diagnosis, ground the antenna base to the
vehicle body. Do not hold the mast. |
| • | Coated bolts and screws may be poor grounds. |
| • | Use a braided ground strap when you apply a ground. Keep the ground
strap as short as possible. |
| • | Use aluminum foil tape or nickel tape in order to shield against
magnetically induced interference when shielding the following components: |
| - | Most hoses are conductive unless the hoses have a white stripe. |
| • | Vary the following ground techniques for optimum grounding results: |
| - | Add a ground at both ends of the tape. |
| - | Add a ground to just one end of the tape. |
| - | Do not add ground to the tape. |
| • | Complete the following steps when shielding a harness with tape: |
| - | Attach a ground strap to the end of the tape. |
| - | Wrap the strap 360 degrees around the tape. |
| - | Secure the other end of the strap to a known good chassis ground. |
| • | If possible, correct any interference at the source of the interference. |
| • | Apply suppression carefully. The following wires can be suppressed: |
| • | Signal wires cannot be suppressed. The following wires are examples
of signal wires that cannot be suppressed: |
| - | The communication circuits |
| • | After you apply suppression, inspect all of the vehicle systems
for correct operation. |
| • | Interference is usually eliminated with the following procedures: |
| • | Use capacitors in order to correct the following conditions: |
| • | Use filters in order to correct the following conditions: |
| • | Whenever possible, make a test harness that includes filters and
capacitors. Always verify that a repair is effective and that the systems
operate correctly before you permanently install a fix. |
| • | Use one of the following capacitor applications for an audible
pop that is induced by a switching operation: |
| - | Add a capacitor across the contacts of the switch. |
| - | Add a capacitor from the hot side of the switch to the ground. |
| - | Add a capacitor to each side of the switch to the ground. |
| • | Complete the following inspections if the condition is present
only when the ignition is in the RUN position and the engine is running: |
| - | Inspect the integrity of the ignition system. Refer to Engine
Controls. |
| - | Inspect the integrity of the engine compartment grounds. |
| - | Inspect for the following conditions that may cause noise or poor
reception: |
| • | Malfunctioning solenoids |
| • | Malfunctioning system components |
| - | Inspect the integrity of the ground for the component that is
causing the complaint. |
| • | Perform the Antenna System test for noise or poor reception. Repair
the system as needed. |
Generator Whine Concerns
| • | Inspect the ground terminal on the battery. |
| • | Inspect for coated mounting bolts on the generator bracket. |
| • | Inspect for a faulty mounting of the generator to the engine. |
| • | Verify that all of the ground straps between the engine and the
frame are clean and tight. |
| • | Complete the following repairs as needed: |
| - | If the noise is still present, inspect the charging system. Refer
to Charging System Check in Engine Electrical. |
| - | If the charging system is functioning normally, refer to any technical
service bulletins on generator whine. |
| - | Install a filter GM P/N 1224205 in the battery feed
to the radio. |
| - | If the noise is still present, install the filter with the following
variations: |
| • | Install the filter with the single wire side toward the radio.
Attach the ground wire to a good ground. |
| • | Remove the ground to the filter. |
| • | Reverse the filter so that the two wire side is toward the radio
and the ground wire is attached to a good ground. |
| • | Remove the ground from the filter. |
| - | If the noise is still present, install another filter GM P/N 1224205
in the ignition feed to the radio. |
| - | Install this filter using the same variations as in the first filter. |
| - | If the installation of this filter causes delays when the radio is turned
ON/OFF, or if the installation causes other performance concerns, complete
the following steps: |
| • | Install a 0.47 mF capacitor to ground in the filter's place. |
| - | Remove any unneeded filters after the repair, before you reassemble
the vehicle. |
Radio Noise
Use a noise sniffer in order to aid in diagnosing the radio noise.
| • | Inspect the radio reception in an area that is free of the following
conditions: |
| • | Ignition noise on FM may indicate that the electronic ignition
(EI) system is defective. Refer to Electronic Ignition System Diagnosis in
Engine Controls. |
| • | Inspect the antenna coax connectors for the following conditions: |
| • | If you use a test antenna, ground the base of the test antenna
to the vehicle body. |
| • | Coated screws or bolts can act as a poor ground. |
Notice To Technicians
Electromagnetic interference (EMI) can cause a fewer number of stations
to be received in one of the three modes. Various vehicle components may cause
EMI. EMI may cause of the differences in reception.
Inspect for components that are powered up in the three various key
positions. This action will eliminate some sets of conditions. For example,
if the same number of stations are received with the engine running as when
the engine was off, active components with the engine running are not causing
interference.
- Determine the type of audio complaint.
- Attempt to duplicate the condition:
| • | Play a known good CD or cassette. |
Use and Construction of a Noise Sniffer
Use the noise sniffer along with the vehicle's radio in order to locate
hot spots which generate radio noise interference. These hot spots can be
found in the following locations:
| • | Between the hood and the windshield |
Make the sniffer from an old piece of antenna lead-in from a mast or
a power antenna. Use the longest piece of lead-in available.
Make the noise sniffer as shown. The 2 in section with the black
coating and the braided shield stripped back becomes the antenna when the
sniffer is plugged into the radio's antenna socket. Use the sniffer in order
to probe and search out hot spots.
Perform the following steps in order to use the noise sniffer:
- Tune into the complaint noise.
- Disconnect the antenna.
- Plug the sniffer into the antenna socket.
- Turn the radio volume up.
- Search for the noise source.
Keep your fingers off the 2 in probe.
When checking for noise on a wire, achieve best results by placing the
sniffer parallel to the wire.
Customer's Tips
How to Enjoy FM Stereo
| • | Select stations within range. The best FM fidelity is obtained
from stations within a 10-40 mile range. Beyond that range, noise
or the flutter may begin to appear due to the line of sight range limitations
of FM signals. Move the treble control down (or to the left) in fringe areas
in order to reduce the treble response. On EQ radios, slowly slide the 10K
control down. |
| • | Realize that tall structures can interfere with signals. Tall
buildings or hills can cause shadows or cancellation of FM signals. This is
similar to the ghost or flutter effect seen on television sometimes when
airplanes are flying in the vicinity. The interference will sound like a
pop or a momentary hiss. Reduce the treble or the 10K setting to a lower
volume in order to reduce interference by tall structures or hills. |
| • | Interference can occur from another radio station. Although the
circuits in Delco receivers are the most advanced available, there are rare
instances when one station will be interfered with by another station. This
only happens when the stations are on almost the same frequency and certain
geographical criteria are present. Select another station or switch to a
tape in order to solve the problem of interference from another station. |
How to Enjoy AM
AM does not have the flutter characteristics of FM. However, AM radio
is subject to interference from the following:
You can reduce noise in the following ways:
| • | Move the treble control down. |
| • | Tune into a stronger station. |
