Cell Phone - Seat Belt Microphone Overview
91 Belt Microphone Overview91 11 00
2026851/1
July 19, 2011
Affected Vehicles
Condition
This Technical Bulletin provides an overview of the seatbelt microphone operation in applicable vehicles.
Technical Background
Beginning with the R8 Spyder, and expanding to R8 Coupe vehicles after CW 36/2010 production, seatbelt integrated microphones (belt mics) are now present to increase call quality and system responsiveness.
The inclusion of these microphones offer several advantages over standard roof microphones:
^ Optimized hands-free quality, irrespective of body height, seat position and vehicle type
^ Constant speaking distance of 10-15 cm
^ Ideal positioning even in vehicles where no conventional positioning is possible (Cabriolet, Roadster).
^ Only slight wind turbulence at the microphone position
^ Very high signal to noise ratio
^ Voice operation even with convertible top open
The belt mics are controlled through the belt microphone control module J886 (Address word A6). There are belt mics in both driver and front passenger seatbelts. In equipped vehicles, J886 controls the belt mics as well as the standard roof microphone, and is powered with a microphone phantom voltage supplied from the telephone control unit R36.
The system automatically switches between the roof microphone and the belt mics based on the seatbelt buckle status:
Driver:
^ Seatbelt not latched: Only roof microphone is active
^ Seatbelt latched: Only belt microphones are active
Front Passenger:
^ Seatbelt not latched: Only driver seat belt mics are active or roof microphone is active (depending on driver seat belt latch position)
^ Seatbelt latched and passenger airbag disabled: Only driver seat belt mics are active or roof microphone is active (depending on driver seat belt latch position)
^ Seatbelt latched and passenger airbag enabled: Driver and passenger belt mics are active.
Production Solution
Not Applicable.
Service
Diagnostic Tips:
^ Vehicles equipped with belt mics always feature a microphone in the roof module on the driver side (for making calls when seat belt is unlatched).
^ The seatbelt microphone control unit is switched on and off by the microphone phantom supply from the telephone control unit.
^ Only one of the three belt mics is active at any one time. This is selected by the seatbelt microphone control unit based on the strongest sound level and the best signal quality.
^ The seatbelt microphone control unit contains a relay that controls toggling between the roof microphone and belt mics.
^ If the seatbelt microphone control unit cannot be addressed via diagnosis, the microphone phantom supply from the telephone module may be defective (i.e. the telephone control unit may be the cause).
^ If the seatbelt microphone control unit is faulty, the system will automatically connect to the microphone in the roof module to allow the call to continue.
^ The seven microphones (6 belt, 1 roof) can be diagnosed individually (for short circuit and interruptions) through MVBs in J886.
Warranty
This TSB is informational only and not applicable to any Audi warranty.
Additional Information
All parts and service references provided in this TSB are subject to change and/or removal. Always check with your Parts Department and service manuals for the latest information.