In most cases the check engine light is triggered by an oxygen sensor failure but can also be triggered by rich mixture, lean mixture, fuel control module issues or something as simple as a loose gas cap. Replacement of the oxygen sensor(s) is fairly easy. To remove the sensor you simply take a 7/8 wrench and loosen the oxygen sensor by unscrewing it counter clockwise. Make sure you unplug the connector first.
NOTE: You can also use the Universal sensors to replace the factory sensor. The only difference between the Universal sensor and the factory sensor is that the universal sensor only has about 12 inches of wire that you will have to splice into your existing harness from the old sensor.
Thanks to Yuri for contributing to this FAQ!
"Check Engine" light came up on my '98 900s for no apparent reason while I was driving on the highway. The car continued to run fine. Then one day I had to remove the battery from the SAAB in order to start my project car, when I put the battery back into SAAB the "Check Engine" light was off and hasn't come on since. So it appears that sometimes disconnecting the battery allows the "Check Engine" light to reset.
Thanks to Kannan for contributing to this FAQ!
Check engine light in 97 saab 9000 came on and codes read misfire in cylinder. Disconnecting the battery corrected it temporarily and final fix was by changing DI cassette. This even though the DI cassette passed the upside