97 Blazer, Service Engine Light Problem?

The Service Engine light on my 97 Blazer with the 4-6L V-6 comes on and goes off repeatedly, mostly on. It has been on the computer both with the light on and with it off. There are no codes shown, either active or in history at either time. All the sensor readings were checked and were within the proper ranges.... show more The Service Engine light on my 97 Blazer with the 4-6L V-6 comes on and goes off repeatedly, mostly on. It has been on the computer both with the light on and with it off. There are no codes shown, either active or in history at either time. All the sensor readings were checked and were within the proper ranges. I know the owner's manual says that changing brands of gas can make it come on, so I have tried staying with one for several weeks at a time with no change.

Does anyone have any idea what can be doing this?

The only other things not right are the fuel gauge and the outside temperature repeater above the window. Could these be related?
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