GM Service Manual Online
For 1990-2009 cars only

Checking Radio Antenna Mast


Object Number: 888561  Size: FH

Unplug the antenna lead-in at back of radio and plug a test antenna into the radio. Make sure the test antenna base is grounded to the vehicle chassis. Do not touch the mast. Check the radio reception in an area away from tall buildings, metal structures, power lines, fluorescent lighting, and power tools. Tune to high and low ends of the dial on both AM and FM, checking weak and strong station reception. Refer to System Performance Check - Noise or Poor Reception . If reception is OK, the problem exists with antenna and/or its lead-in antenna cable. Verify the antenna mast is at the appropriate torque. If reception is still poor with test antenna, check for aftermarket equipment that may be causing complaint.

Checking Antenna Lead-In Cables

In case of continued reception or noise complaints, always check the lead-in antenna cable with a digital multimeter (refer to the following illustration and chart). If long jumper leads are not available, check center conductor continuity by jumping the antenna coax cable to ground and checking for continuity from the center conductor at radio to ground. The type of coaxial cable used is RG-62/U.

When checking resistance, cautiously wiggle the antenna lead-in tip and antenna coax cable. Consistent readings from table should always be obtained. If not, some portion of the antenna lead-in is intermittent and lead-in should be replaced. Also try the following:

    • Running a braided ground strap to the antenna lead-in.
    • Changing the antenna lead-in.
    • Disconnecting the antenna lead-in to check resistance.
    • Check antenna in-line connection for corrosion or poor connection.