GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firefly (Canada) 🢒 Body and Accessories 🢒 Entertainment 🢒 Diagnostic System Check - Radio/Audio System
  1. Verify the customer complaint.
  2. Follow the radio service procedures.
  3. If technical assistance is required, have all the pertinent information available before placing the call.

Identifying Concerns
    • Examine the technical service bulletins. Use the dealer communication system for any applicable preliminary information (P/I) for customer concerns.
    • Inspect for stored diagnostic trouble codes. Refer to Driveability and Emissions in Engine Controls.
    • For reception concerns, determine if the station is obtainable in the customer's listening area.
    • When you test for audio reception/noise, position the vehicle outside of the building with the hood down.
    • Duplicate the customer's complaint before trying to diagnose the system. Instruct the customer to demonstrate the condition. Test drive the vehicle with the customer, then test drive a similar model (with a similar audio system) in order to determine if the condition is abnormal.
    • Before you diagnose the condition, identify the following:
       - The components
       - The component features
       - The customer's complaint
    • Determine if any aftermarket equipment is installed on the vehicle. Disconnect the aftermarket equipment in order to determine if the customer's complaint still exists. Follow GM guidelines for the installation of aftermarket components.
    • Perform the following steps in order to indentify a noisy component:
        1. Identify the ignition key switch position in which the noise appears:
   • The accessory
   • The key ON engine not running
   • The key ON engine running
        2. Remove the fuses one at a time until the condition is eliminated.
        3. Mark the complaint fuses and reinstall all the fuses and the circuit breakers.
        4. Refer to Power Distribution and Fuse Block Details in Electrical Diagnosis in order to identify all the systems and the components powered by the complaint fuses.
        5. Disconnect the components powered by the complaint fuses one at a time until the condition is eliminated and the noisy component is identified.
        6. Inspect the ground integrity of the questionable component.
    • An interference condition is NOT necessarily an audible noise.
    • Most noises can be found on weak stations near the low end of the band. This is considered to be a normal condition.
    • Ignition noise on FM could indicate that the ignition system is faulty.
    • The following conditions may induce noise or poor reception:
       - Malfunctioning and marginal components
       - Relays
       - Solenoids

Corrective Action
    • Use the proper tools for diagnostics and repairs.
    • Follow the ESD guidelines.
    • Use the following noise suppression devices:
       - 220 mF (50V) capacitor GM P/N 1227895
       - 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
       - 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 GM P/N 12091511
    • Utilize the test tape/CD Diagnostic Kit J 39916-A in order to optimize the proper audio diagnostics.
    • If you must return the radio to the service center, describe the symptoms on the warranty form accurately. Send a copy of the service writer check list with the unit.
    • Do NOT leave a CD or a tape in the car. Extreme heat can cause permanent damage.
    • Cassette tapes could be damaged if the tapes are not stored in the case. The vibration in the vehicle can cause the tape to unwind inside the cartridge.
    • Use diagnostic charts in the DE SSG.
    • Before removing the speakers, inspect all the connectors and the wiring to the speakers. Examine the connectors for bent or loose pins.

       Important: 
   • Inspect the antenna coax connectors for corrosion, or for bad connections or crimps. Route the coax separately from the other wires. Shield the antenna coax interconnections with aluminum or nickel tape as described in the DE SSG.
   • Inspect all of the vehicle grounds, NOT just the radio and the antenna grounds. Refer to Antenna Diagnostic Check .

    • If you use a test antenna in diagnostics, ground the antenna base to the vehicle body. Do NOT hold the mast.
    • Coated screws or bolts are poor grounds.
    • Always use a braided ground strap when applying grounds. Ensure that the ground strap is as short as possible.
    • When shielding the following components, use aluminum foil tape or nickel tape in order to shield against magnetically induced interference:
       - The dashboard
       - The wires
       - The hoses (most hoses are conductive unless they have a white stripe)
    • For optimum results, try varying the following techniques:
       - Add a ground at both ends of the tape.
       - Add a ground to just one end of the tape.
       - Do not add a ground to the tape.
    • 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.
    • Suppress the interference at the source.
    • Use care when suppressing interference. Battery wires and ignition wires can be suppressed. But signal wires such as the following cannot be suppressed:
       - The sensor outputs
       - The clock
       - The communication circuits
    • After adding suppression, inspect all vehicle systems for proper operation, even those not related to the audio system.
    • Shielding/grounding or suppressing can usually eliminate interference.
    • Capacitors work best on switch pops and low frequency noise. Fillers work best on high frequency whines and static.
    • Whenever possible, make a test harness that includes fillers and capacitors. Always check the effectiveness and operation before permanently installing a fix.
    • For an audible pop induced from a switching operation, apply the following cpacitors:
       - Add a capacitor across the contacts of the switch.
       - Add a capacitor from the hot side of the switch to ground.
       - Add a capacitor to each side of the switch to ground.
    • If a complaint conditon is only present with the ignition key in the RUN position, and the engine running, perform the following inspections:
       - Inspect the integrity of the ignition system (proper spark plug wire routing, no misfiring, etc.). Refer to Ignition System in Engine General Information and Mechanical Diagnosis.
       - Inspect the integrity of the engine compartment grounds.
       - Inspect for the following for a malfunction which may be inducing noise or poor reception:
   • Relays
   • Solenoids
   • Other components
    • Inspect the ground integrity of the faulty component.
    • For noise or poor reception, refer to Antenna Diagnostic Check and make the necessary repairs.

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.
    • Ensure that all of the ground straps between the engine and the frame are clean and tight.
    • Select from the following list of repair procedures:
        1. If the noise still exists, inspect the charging system. Refer to Charging System in Engine General Information and Mechanical Diagnosis.
        2. If the charging system functions normally, examine the technical service bulletins on generator whine.
        3. Install a filter GM P/N 1224205 in the battery feed to the radio.
        4. If the noise is not eliminated, install a filter with the following variations:
             4.1. Install the filter with the single wire side toward the radio and the ground wire attached to a good ground.
             4.2. Remove the ground to the filter.
             4.3. Reverse the filter so the 2-wire side is toward the radio with the ground wire attached to a good ground.
             4.4. Remove the ground from the filter.
        5. If the noise still exists, install another filter GM P/N 1224205 in the ignition feed to the radio.
        6. Install this second filter using the same variations as the first filter.

If the installation of this filter causes ON/OFF delays or other noticeable performance concerns, remove the filter and install a 0.47-mF capacitor to ground.

        7. Remove any unneeded filters before reassembling the vehicle.
        8. Refer to System Check.