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PCM 3.1 in endless reboot

  • 2016
  • Cayman GT4
60 500
Electrical and Electronic
New York, 
New York

As of last week the PCM in my GT4 has been going through an endless reboot, but the screen itself doesn't turn on at all. You can see the illuminated buttons flash and you can hear the speakers as though they're being cycled on and off, so it sounds as though it's rebooting but never actually getting to the boot screen itself. I've pulled the fuse a couple times, leaving the car overnight, then plugging it back in—this has worked a couple times, but once I turn the car off and back on again the PCM goes into the first state I detailed (i.e. screen off, buttons flashing, speakers cycling). Some searching online yielded a couple similar cases, however the individuals posting about it never followed up with if/how it was resolved. [Note that this is seemingly unrelated to the May 2020 XM radio issue: PCMs affected by that were still able to boot and function for a time before rebooting. It's worth noting that I've all the same tried the reset procedure for the XM issue just in case, but it hasn't helped].

So it seems the only solution is likely a full PCM replacement. The independent shop where I get my car worked on does race prep, so they have a ton of PCM 3.1 units sitting around from cars they’ve stripped out and converted for race use, and so I can source a replacement from them for cheap, however we don’t quite know what the procedure would be for coding (they do strictly mechanical work, not radios and such). Would this be something I’d have to take it into a dealership for, i.e. recoding the unit to the car? And would they be none too pleased that I’m bringing in a 3rd party replacement unit instead of buying it new through them? I'm just trying to figure out how best to navigate these waters.

Thanks to anyone that might be able to provide some information on this!

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