Odb2 will not pwr up my snapon scanner on a 95 saab 900s

The OBDII Scanner will turn the ignition key forward but don't start vehicle and turn all lights and radio off and heater off. And plug the scanner in. Then it will run the codes and tell you what code(s) are write them down. Then you will hit the erase button to reset your engine light. If the light goes back on you have a problem it should stay off up to 50 miles if not then have your vehicle checked out usually it could be your O2 sensors or a MAF Sensor "MASS AIR FLOW SENSOR" that is faulty and or your intake tubes are loose allowing too much air flow in to the engine if this happens your car will be running too lean.

Good Luck!