Saab Problems? Ask a Mechanic for Answers ASAP
Saabs sold in the US adhere to OBD-II protocols, which means that if you're familiar with those protocols, then you should be fine.
P0037 sets when Oxygen sensor heater circuit voltage is not detected by the onboard computer (PCM) - this is usually caused by a blown fuse #2, a bad O2 Heater relay, or shorted or open circuit/wires between the relay and the sensors.
P0300 sets when the PCM detects random misfires that cannot pinpoint to any specific cylinder - probably a result of P1312 in this particular case.
P1312 sets when the PCM detects more than one cylinder firing at the same time - this usually means bad coils.
I can guide you through a systematic diagnostic process to confirm all these faults. Just please be aware that you will have to use tools such as a Tech-II or equivalent scan tool and an automotive multimeter to execute some of the diagnostic procedures.