For mid 2000s, the car is self monitoring so an emissions check is just a visual once over to ensure no physical tampering and a computer readout of emission readiness monitors + firmware checksum for digital tampering.
Right, and even the monitors can differ. If a car wasn't made with a certain monitor, that's one less check it has to pass. One of my cars had issues with passing SAI, the other has N/A for that.
