It's quite possible your vehicle's aftermarket radio is causing the smog machine the inability to properly communicate with your vehicle ECU.
Saab factory stereos are capable of self diagnostics in most of their vehicle models. In essence these are smart radios capable of sending fault information to the vehicle's ECU (engine control computer) as well as important speaker volume data, radio preset information, and various other media and control function.
In the early days a "k-line" connection was used to connected the radio to the ECU, and more recent computer systems use the CAN (Controller Area Network) system via the CAN-high and CAN-low signal wires.
In either case an improperly installed aftermarket stereo will severe ECU communication and trigger the Malfunction Indicator Lamp on; causing the vehicle to fail the smog test.
We recommend resorting to the original factory stereo, or finding a local professional aftermarket stereo installer who can wire your Saab's radio to function properly with the ECU. It can often be done by installing an interface adapter between the aftermarket stereo and ECU. Search or ask about "Smart Radio Wiring Harness" for newer Saab models.