Reduced Power Mode on 2003 Saturn Vue

What can cause my 03 saturn vue 2.2 4 cyl. variable speed transmission to go into the reduced power mode? Sometimes the check engine light comes on and sometimes it don't.Sometimes I can stop, switch off and restart and it will run normal for a while and sometimes it won't. The computer never stores any trouble codes when this happens.Can anyone help answer this?

Asked by for the 2003 Saturn Vue
If the Check Engine Light comes on the computer has to store a code unless the computer has a fault or it looses power required to store codes in the computer. A professional grade scan can read stored codes, pending/soft codes, modes six diagnostic data and live sensor data. What scan tool is being used to retrieve codes.
Thank you for your answer Patrick. I have 2 code readers. One is an inexpensive Actron that does nothing but retrieve and erase codes. The other is an Inova fairly expensive, by my standards, that retrieves codes, pending codes,abs codes, checks the status of the im moniters etc. Both scanners say there are no codes stored in the computer. The inova is telling me that all the moniters have gone through their cycle and all are working. So you think it may be the computer? I really appreciate your takeing time for this. Thanks. Prentice Price.