Adding Bluetooth to a Porsche 997.1

All Porsche 997.1 cars came with Porsche’s PCM 2.1 multimedia system. PCM 2.1 is a modular system that in its base version contains a radio and on-board computer. It can be expanded with a navigation computer, CD changer, phone module, and better audio amplifiers (such as a Bose system). All of these are linked to the PCM head unit via an optical MOST bus. Unfortunately, PCM 2.1 offers neither Bluetooth connectivity nor an AUX audio input. This is an omission that I really don’t understand, as the COMAND NTG 1 of my Mercedes W211 from the same era has both. The available phone module requires a second SIM card instead of being able to connect to the driver’s phone.

Throughout the years there have been several systems to at least partly solve this problem. Some of these use the ever-popular solution of including an FM transmitter, which is suboptimal at best. Dension offer a unit that ties into the MOST bus, but it is quite expensive. The most attractive solution to me is the Mr12Volt MOST box, which is quite affordable, yet includes Bluetooth for both handsfree calling and audio streaming, an AUX port, and music playback from USB sticks and SD cards. The only solution more powerful is a new head unit, either from a third party or Porsche’s PCCM+, and this is the way to go if you want Apple CarPlay/Android Auto.

The Mr12Volt Box presents itself to PCM as CD changer. It requires the MOST bus to be active, which is the case if you car already contains one of the additional systems (navigation, CD changer, Bose audio, or phone). If not, the CD changer functionality will have to be activated with the PIWIS software. There’s a lengthy and very useful thread about the installation on Rennlist. There are essentially three possibilities for the installation:

  1. Close to the PCM unit, drawing power from the PCM wires itself or the 12V port in the passenger’s footwell (if present).
  2. Replacing the CD changer in the frunk.
  3. Replacing the phone module under the right front seat.

Each option has its advantages and disadvantages with regard to access to power and (microphone) cable routing. If you don’t need the microphone, installation in the CD changer’s location (if present) is the easiest, as you then don’t need to pull out the PCM or fiddle under the right seat. In all cases, CD changers and phone modules need to be taken out of the MOST loop. An existing phone module needs to be coded out, otherwise there will be an error message during each start.

The stock microphone is located behind the steering wheel, but this is not usable with the Mr12Volt box. One option for placing the microphone is in the instrument cluster. Enfig make a microphone that fits into the location behind the steering wheel.

In my car, I decided to go for the frunk. I removed the CD changer, soldered pins onto the ends of the Mr12Volt power cable, and inserted those into the CD changer power plug (brown is ground, red/green is 12V). The Bluetooth box currently dangles in the frunk, I might design and 3D print a bracket for it.

I right away got the message that the phone is not available, despite the phone module still being connected. This will have to be coded out and I will disconnect the phone module. I haven’t decided yet how to deal with the microphone.

The phone module is located under the right seat. Two 10mm bolts are hidden away under the carpet, removing these allows for removal of the bracket that holds the phone module. This is held in place by two more 10mm bolts and three cables – the antenna, MOST bus, and power. The latter two require depressing parts of the connector. I could only get the antenna connector off by prying it off with a screwdriver. I then wrapped some foam around the connectors and secured it with a tie wrap to keep the loose connectors from rattling.

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