PASM failure

[boxsters987]

04/2006 Boxster S in the UK just out of warranty. The onboard computer tells me 'PASM indicator faulty' and Durametric gives error code C156 'Communic. PASM control unit under the PSM section'. The PASM and Sport buttons don't work and it feels like the car has gone in to sport mode which I believe is the failsafe setting.

Has anyone got more details of what causes this error and what I need to do to rectify it? Where is the PASM control unit (so that I can check the connectors) and if I need to replace it can I just plug-and-go or will the ECU need to be reprogrammed to recognise it?

Thanks.