Possible cause of fault

• An optical (optical waveguide) or electrical (PCM2) open circuit in the ring
• PCM2 in production mode
• An optically/electrically faulty MOST control module is connected to the MOST

The MOST optical waveguide is connected to the following control modules:

• PCM2 as of model year 2003 
• CD changer 
• Amplifier 
• Telephone/telematics 

Fig 1: Identifying Communication Circuit - 8009 PCM2, MMI

Courtesy of PORSCHE OF NORTH AMERICA, INC.