Or the speaker coil(s) themselves may have opened up.

Not sure if there is a crossover for the speakers in question.

Might try to isolate the speaker wires from the amplified and send a test tone or other signal to the speaker(s) to see if these still work.

I use a wire tracer tone generator for testing/identifying speakers, but I have a number of these on hand.

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2008 4.8i Black with Tabacco. Black Y-spoke wheels and shadowline trim.