1) Check the Subwoofer for continuity - At the subwoofer, one at a time, test the terminals for Continuity using your Digital Multi-Meter; if your DMM doesn't have a Continuity test, use the Resistance, or Ohms, test and check for Resistance in the Subwoofer Coil (be sure to disconnect the subwoofer wiring before performing these tests).
2) If they test out good, hook the wires back up and test the terminals at the terminal cup or at the Amp hookup if you didn’t use a terminal, don't hook it up to the amp yet. Sometimes the wiring inside the box can be a problem if it has come loose, or isn't making a great connection.
3) If you have a Sub or multiple Subs with Dual Voice Coils, or multiple Subs with Single Voice Coils, make sure your wiring is correct by checking here:
4) Make sure there are no Hi-Pass filters, crossovers, or multi Channel switches enabled.
5) Replace your RCA cable/s with known working RCA cable/s from the Source/Head Unit to the Amplifier/s.
6) Check your Head Unit settings; make sure the Bass is turned up and/or the Subwoofer setting is turned On.
7) If you are still getting no or low output, try plugging in an MP3 player or CD player using a headphone to RCA adaptor and check for sound output. If there is still no or low output, your Amplifier outputs are probably burned out.
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