Early versions of the OBDII port, like the OBDI port before it, have a 12V peak to peak tach signal on pin 9. This is from an early Boxster.
But at some point the output of this pin changed. My 07 997 Turbo, for instance, doesn't have this signal.
Does anyone know when the pin 9 signal stopped being a square wave pulse signal on the Boxster, and on the Cayman?