Cobra 29LX "CB Antenna Warning"

I'm having problems with my cobra 29. It reads CB antenna warning. I'm pretty sure I just need to upgrade the coax but I just want other opinions (preferably professional opinions). I have a Wilson 2000 trucker antenna on an "XL mount". The coax is RG-58 9' long and runs through a little opening of the driver side door and continues behind the dash and then up to the radio. Here are some pics so you have a general idea.







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Cobra 29LX "CB Antenna Warning"