convertor

Hi, My ibiza 1.2 (2002) engine light keeps coming on every 100 miles or so and the fault code given is: 16804 Catalyst system: bank 1: efficiency below threshold - Im not sure if there is any way to test if the cat is at fault or if its one of the sensors, but has anyone tried using anything...

Am trying to get an amp running of a standard Ibiza Mk3 HU, I have the amp powered up but am getting no signal from hu to amp via a high/low level convertor, are pre-outs a better:confused: way to get a signal?