bdh3801

We have a b8.5 s4 with B&O in at our shop that had optical issues on the MOST system. Only code present was the optical disconnect code stored in the gateway module and we had no other function on the MOST loop. We went through the standard diagnosis with our optical loop. We found when looping out the B&O amp, we regained MMI function. We checked power and ground to the AMP and verified both were good with no abnormal resistance. So, we went ahead and replaced the AMP with no success. We still have no MMI but no longer have an optical circuit codes and we now have access to the Radio module and the 5f main mmi unit. No notable codes are present in any of the modules except for an antenna fault in the Radio. We also verified the functionality of the replacement AMP by installing it into a family member’s vehicle. Besides the component protection, the functionality was perfect. Please help, I am losing my mind.

bdh3801

Quick note,
When performing an MMI reset, I can get access to the AMP with the scanner (for only about 5 seconds). The only codes stored in the AMP before it going back offline is just component protection faults.