Important: Electromagnetic interference (EMI) can cause a fewer number of stations to be received in one of the three modes. Various vehicle components can cause the EMI. This may be the cause of the differences in the reception. Check for components powered up in the three various key positions. This may eliminate the engine running components, the ignition on components, etc. For example, if the same number of stations are received with the engine running as when the engine was off, the components active with the engine running are not causing the interference. Perform the following procedures:

1. Verify the customer concern.
2. Follow the radio service procedures.
3. If you require technical assistance, have all of the pertinent information available before placing the call.

1. Look for technical service bulletins. Read the Dealer Communication System for any applicable preliminary information (P/I) for customer concerns.
2. Inspect for stored diagnostic trouble codes. Refer to Diagnostic Trouble Code (DTC) List in Engine Controls -- 4.3L or Diagnostic Trouble Code (DTC) List in Engine Controls -- 4.8L, 5.3L, 6.0L.
3. For reception concerns, determine if the station is obtainable in the customer's listening area.

In order to test for audio reception and noise conditions, perform the following steps:

1. Position the vehicle outside of the building with the hood down.
2. Duplicate the customer's concern before trying to diagnose the system.
3. Have the customer demonstrate the condition.
4. Test drive the vehicle with the customer.
5. Test drive another similar model vehicle with a similar stereo system in order to do a comparison of the vehicles.

This step will help to determine if the condition is abnormal.

6. Identify the components, the features, and the customer's concern before diagnosing the system.
7. Determine if any aftermarket equipment has been installed in the vehicle.
8. Disconnect the aftermarket equipment in order to determine if the customer's concern still exists.
9. Follow the GM guidelines in order to reinstall the aftermarket components. Refer to the most current bulletin available.

In order to identify a noisy component, perform the following steps:

1. Identify the ignition key switch position in which the noise appears, such as ACC, or KEY ON engine running/not running.
2. Remove the fuses 1 at a time until the condition has been eliminated.
3. Mark the fuse(s) in order to install all the fuses and the circuit breakers.
4. Identify all the systems and the components powered by the fuse(s). Refer to Wiring Systems.
5. Disconnect the components which are powered by the fuse(s) 1 at a time until the condition has been eliminated and the noisy component has been identified.
6. Inspect the ground integrity of the concern causing component.