Are both fans coming on the moment the car starts up or after a few minutes or after the A/C is engaged. Did you have any A/C work done or r/r a component. I am looking at the schematic and it is pretty straight forward. I am just wondering if it is an input that the PCM is reading incorrect.
The ones that I canthink of is:
ECT- exceeds 113'c fans come on
A/C pressure enable - pressure is greater than 275 psi fans come on

Also if you have fbody service shop manual, look on page 6-1123 for electrical cooling fan disc. It gives more info than Ican type.