GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Classic - 4WD 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 Radio Poor Reception

Schematic Reference: Radio/Navigation System Schematics

Diagnostic System Check - Entertainment System

Always perform the Diagnostic System Check before proceeding with these diagnostic procedures. Refer to Diagnostic System Check - Vehicle .

Antenna System Test

Important: Always zero out the DMM before taking a resistance measurement in order to ensure an accurate reading.

  1. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection .
  2. Disconnect the antenna lead-in connector from the radio receiver.
  3. Measure the resistance from the negative battery cable to the coax outer conductor connector.
  4. The resistance measured should be 0.2 ohm or less.
  5. Test the following when the resistance is greater than 0.2 ohm:
    6. • Base of the antenna for a poor connection to body ground
    • The coaxial cable interconnects for a poor connection or corrosion.
    • Test for an open or high resistance from the battery negative cable to the body. Refer to Circuit Testing and Wiring Repairs .
  6. After finding and correcting the condition, operate the system in order to verify the repair.

Perform the Antenna Checking Procedures after confirming the integrity of the antenna ground.

Antenna Checking Procedures

Perform the following tests for the type of antenna on the vehicle.

Mast Antennas

Unplug antenna lead-in connector from radio receiver and plug a test antenna into radio. Make sure antenna base is grounded to the vehicle chassis and keep hands off the mast.

Check radio reception in an area away from electrical interferences. Tune to several weak and strong AM and FM stations. If the radio reception improved, the problem exists with the antenna and/or lead-in cable. If the reception is still poor, refer to Audio System Troubleshooting Hints .

Important: Always zero out the DMM before taking a resistance measurement in order to ensure an accurate reading.

Mast Antenna System
Object Number: 782084 Size: MF
(1)Negative Battery Cable
(2)Coaxial Cable Conductor - Radio End
(3)Coaxial Cable Metal Outer Shield - Radio End
(4)Coaxial Cable Metal Outer Shield - Antenna End
(5)Coaxial Cable Conductor - Antenna End
(6)Antenna Base
(7)Antenna Mast
(8)Antenna Coaxial Cable

Ohmmeter Probes At Points

Resistance Measured In Ohms

1 and 3

Less than 0.2

1 and 4

Less than 0.2

1 and 6

Less than 0.2

1 and 2

Infinite

1 and 5

Infinite

1 and 7

Infinite

2 and 3

Infinite

2 and 4

Infinite

2 and 6

Infinite

3 and 4

Less than 0.2

3 and 6

Less than 0.2

3 and 5

Infinite

3 and 7

Infinite

Refer to the table when testing the antenna and/or lead-in cable.

  1. Measure the resistance from the coax center conductor to antenna mast.
  2. Total resistance from end to end of center conductor:
    3. • RG-58/RG-59 type cable--Less than 0.20 ohm
    • RG-62/RG-62M type cable--Less than 3.5 ohm
  3. When checking the resistance, cautiously wiggle the lead-in tip and cable. Refer to Testing for Intermittent Conditions and Poor Connections .
  4. Measure the resistance from the cable center conductor to metal case.
  5. Replace the antenna and/or lead-in cable when the above readings are not obtained.

Some vehicles come equipped with a pre-amplified AM/FM antenna that is powered by SW 12+. If the antenna loses this power source or a ground, poor reception can occur.