WHY IS THE SERVICE ENGINE LIGHT ON IN MY SATURN??

The Check Engine light will light when the ECU stores a trouble code.
Counting the Flashes
To retrieve trouble codes, turn the ignition key to the "on" position with the engine OFF.
The Check engine light will flash many short blinks. The total number of blinks equals the code number. For example, flash,pause, flash,flash = code 12.If more than one code is stored, the Check engine light will flash the codes in sequence (lowest to highest) with a pause between each code. The codes will repeat until the key is turned to the OFF position.

11 Transaxle codes present 12 Diagnostic check only 13 Oxygen sensor circuit 14 Coolant sensor/high temperature 15 Coolant sensor/low temperature 17 PCM fault - pull-up resistor 19 6X signal fault (92-95 models) 21 Throttle position sensor-voltage high 22 Throttle position sensor-voltage low 23 IAT circuit low 24 VSS circuit-no signal 25 IAT circuit-Temp out of high range 26 Quad driver output fault 32 EGR system fault 33 MAP sensor - voltage out of range high 34 MAP sensor - voltage out of range low 35 IAC - rpm out of range 41 Ignition control circuit-open or shorted 42 Bypass circuit - shorted or open 41/42 IC control circuit grounded/bypass open 43 Knock sensor circuit shorted or open 44 O2 sensor indicates lean condition 45 O2 sensor indicates rich condition 46 Power steeringpressure circit(91 models)open or shorted 49 High idle indicates vacuum leak 51 PCM memory error 53 System voltage error 55 A/D error 58 trans fluid temperature too high 59 Trans fluid temperature too low 66/67 A/C pressure sensor 81 ABS message fault 82 PCM internal communication fault