Don't know! But if you find out do please post a reply as the wife's 2003 has the same problem. The best advice I've seen is to contact the Clarion Service Centre UK who apparently can do a fixed price repair for £65 + £9 P&P ish. That's a lot less then the £500 quid to replace one new, and they also do the security coding issue so it all links up in your car. Only problem is getting the unit out of the dashboard which apparently takes 15 minutes even when you know how...and I don't.
Ken
July 2011
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix in-car audio.