1. Verify the customer complaint.
2. Follow the radio service procedures.

Refer to any technical service bulletins.

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:

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:

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:

Use the correct tools for diagnosis and repairs. Be sure to follow the ESD guidelines.

Use the Test Tape/CD Diagnosis Kit GM P/N J 39916-A to assist in optimizing the diagnosis.

Take the following precautions in order to prevent damage to cassettes:

Complete the following steps before you remove the speakers:

If you test an antenna, ground the antenna base to the vehicle body.

Important: Inspect the antenna coax connectors for the following conditions:

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:

Vary the following ground techniques for optimum grounding results:

Complete the following steps when shielding a harness with tape:

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:

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:

Complete the following inspections if the condition is present only when the ignition is in the RUN position and the engine is running:

Perform the Antenna System test for noise or poor reception. Repair the system as needed. Refer to Radio Antenna Cable Extension Cable Replacement .

Complete the following inspections:

Complete the following repairs as needed:

1. If the noise is still present, inspect the charging system. Refer to Charging System Check in Engine Electrical.
2. If the charging system is functioning normally, refer to any technical service bulletins on generator whine.
3. 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.

4. If the noise is still present, install another GM filter in the ignition feed to the radio.

Install the filter using the same variations as in the first filter.

If the installation of this filter causes turn on or turn off delays or other performance concerns, complete the following steps:

4.1.	Remove the filter.

4.2.	Install a 0.47 mF capacitor to ground in the filter's place.

5. Remove any unneeded filters after the repair before you reassemble the vehicle.

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 items:

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.

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.

1. Determine the type of audio complaint.
2. Attempt to duplicate the condition:

-	Listen to AM or FM.

-	Start the vehicle.

-	Play a known good cassette.

-	Test the switches.

The radio receives battery voltage at all times on circuit 640 through fuse E1-E2 in order to keep the clock and preset memory alive when the ignition is in the OFF position. The radio is grounded through circuit 351. When the ignition is in the ACCY or RUN position:

The radio control switch controls volume, station frequency, and tape functions. The radio control switch receives power through circuit 43. When one of the radio control switches is pressed to the desired function, a network of series resistors allows a different volage output through circuit 1796 to the radio.