So Ive finally found out why my sound is awful and the meridian sound options do not work..my sub is goosed!
No power at all, so I've been looking on ebay for a replacement and I presume the same sub part number CPLA-18808-CA is fitted to the l405 and l494 so it doesn't matter if the new sub has come out of a l405 or a l494 as the part number is the same so, as its interchangeable between cars?

New sub fitted today, still no sound from the new sub?
No error codes from the amp or the sub and the meridian options are still not working , so Im stuck on stereo sound still!

Im really really stuck with this :/ are there any fuses for the sub? I presume if the amp fuse had gone Id have no sound whatsoever?

Does anyone know of any decent Car audio experts east yorkshire way or otherwise my only option is to get a diagnostic from a main dealer

Just had a thought is there anyway that the heated seat and no power to the sub under the seat could be connected?

Im going to take the seat out at the weekend and have a look, is there a way to test the sub wiring for continuity either on the sub or the car to sub wiring?

Finally got to the bottom of this!
Old/New subwoofer all fine - Wrong amp installed - the amps been swapped out at some point for a MID 8 Amp , hence no sub/Meridian options.

Just found one on ebay £275 , so my old amp will be going up for sale shortly