Noise Diagnosis - Corrective Action

^ Use proper tools for diagnostics and repairs.
^ Follow ESD guidelines.
^ Use available 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 1 224205
- 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 braided ground strap GM P/N 12091511
^ Utilize the test tape/CD Diagnostic Kit GM P/N J 39916-A to optimize proper audio diagnostics.
^ If the condition requires the radio to be sent to the service center, describe the symptoms on the warranty form accurately. Along with the warranty form, send a copy of the Service Writer Check List with the unit.
^ Do not leave a CD disc or tape in the car. Extreme heat could cause permanent damage.
^ Cassette tapes could be damaged if not stored in the case. The vibration in the vehicle can cause the tape to unwind inside the cartridge.
^ Before removing speaker(s), check all connectors and wiring to the speaker(s). Examine the connectors for bent or loose pins. Refer to Troubleshooting Procedures. Diagnostic Aids
^ If a test antenna is used in diagnostics ground the antenna base to the vehicle body and do not hold the mast.

Important:
^ CHECK the antenna coax connectors for corrosion or bad connections/crimps. Route coax separately from the other wires. Shield antenna coax interconnections with aluminum or nickel tape as described in the DE SSG.
^ CHECK all vehicle grounds, NOT just radio and antenna grounds. Refer to the antenna diagnostic section.
^ Coated screws or bolts can act as poor grounds.
^ Always use a braided ground strap when applying grounds. Keep the ground strap as short as possible, the shorter the ground strap the better.
^ When shielding the dash, wires, hoses (most hoses are conductive unless they have a white stripe), etc., use aluminum foil tape or nickel tape to shield against magnetically induced interference. For optimum results, try varying the following ground techniques:
- 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.
^ When shielding a harness with tape, attach a ground strap to the end of the tape and then wrap the strap 360° around the tape securing the other end of the strap to a known good chassis ground.
^ Any interference is best corrected by suppression at the source of the interference, if possible.
^ Care should be used when applying suppression. Signal wires (such as sensor outputs, clock, and communication circuits) CANNOT be suppressed. Battery and ignition wires can be suppressed. After adding any suppression, all vehicle systems (even those not related to the audio system) should be checked for proper operation and function.
^ Interference can usually be eliminated by shielding/grounding or suppressing.
^ Capacitors work best on switch pops and low frequency noise. Filters work best on high frequency whines and static.
^ Whenever possible, make a test harness that includes filters and capacitors. Always check the effectiveness and operation before permanently installing a FIX.
^ Recommended capacitor application for an audible pop induced from a switching operation is:
- 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 condition is only present with the ignition key in the RUN position and the engine running, perform the following checks:
- CHECK the integrity of the ignition system (proper spark plug wire routing, no misfiring, etc.), refer to Ignition System. Ignition System
- CHECK the integrity of the engine compartment grounds.
- CHECK for malfunctioning relays, solenoids. or other components which may be inducing "NOISE" or poor reception.
- CHECK the ground integrity of the complaint causing component.
^ For noise and/or poor reception, perform the Antenna System Test and make the necessary repairs.