My 2000 M5 was in for a California smog check. The guys at the shop told me it just wouldn't talk to the smog test computer at all. We suspected that they might have damaged the OBDII port by pulling out my Davis CarChip while the engine was running.

I took the car home and closed the door on the OBDII port (which jumpers a few pins) and drove a few cycles. After this, that the system started broadcasting good data (as recorded by my CarChip)

On a return visit to the shop, the first tech said the M5 OBDII port would still not talk to the smog machine. Fifteen minutes later, a more experienced tech hooked it up, and got an immediate OBDII sync and the OBDII port becan communicating with the smog test machine. The car was too cold to test, so we unhooked it to drive it to temperature. I forgot to close the little door that jumpers pins on the OBDII port when closed. When we returned, the OBDII would not communicate with the smog machine anymore. We ran out of time and plan to try again in two days.

I'll update you all. But have any of you experienced something similar?