To add to the above.............. what you are experiencing is pretty normal.
This is covered inside and out in other threads............... but.............
I recently wrote off my 2007, have bought a 2006. So I am currently checking my fan to ensure it will handle the upcoming summer.
As said above, if someone has changed your settings = who knows? But standard, the fans will run on low whenever they like if climate control "auto" is used. They will run year round, as they run to cool, but in winter, A/C runs to dehumidify as well. Mine is in "auto" forever, as A/C's biggest problem is not being used.
So to test on and off, you need climate control off.
A lot of people talk about "low/med/hi". My cars (both) don't have that, and neither do the wiring diags. They have low and high. The duty cycle for the fans is they can run on low forever, can only run on high for burst. That is "what everyone says", not from any factory source I can find, but it makes sense.
When the fans are on low, they are being run in series. THAT is why so many relays, to reconfig. On high, they get full voltage/are in parallel.
The info most bandy around is - low on 217/103 (all temps in deg F/C) , low off 212/100. High on 226/108, High off 219/104.
My V6 AND the "new" (replacement, so new for me) V8 both come on low as above, at 217/103, BOTH switch off at 210/99. The V6 would only come on Hi rarely, and was more triggered by A/C condensor temp, as my car has NEVER reached 108. It would run for 2 minutes max when it did. I can't get the "new" car to switch on to hi, as winter/too cold here. But I am happy it comes on for Low, will see what happens in summer.
Both cars have the 95 deg stat, I will be changing that to an 82 for the new/V8 when I do a coolant flush the next few weeks. I will leave the fan settings as are, as I don't have the software stuff to change - YET. I know the temp will creep up past thermostat fully open, But I do very little city driving, so car will normally be open road, hence run at 82 deg all day MOST of the time.
While these cars globally have 5 radiator sizes (the US 4 sizes and the HUGE middle East market one), here in Oz they only supplied two rads (apparently), the SRT's get the "max cool" (approx 44 mm, 1- 3/4 inch), and ALL other 2006/2007 etc get the 32 mm (1 - 1/4 inch) "super duty 2" which is the biggest "non SRT" rad, (both my cars have that) so should be ok.............
Finally, be careful when replacing the relays if you need to. They are not just "normal relays"; many aftermarket spotlight relays have two terminals that are both "normally closed" contacts, so a double up of "output". So you can run two spotlights. Wheras the fan relays used on our cars use BOTH normally open AND normally closed contacts, ie, use it as a changeover. The fan current path on low runs through BOTH "open" contacts. So a wrong relay will defeat the low speed running, and is also why people get caught out when they energise the relay/test the closed contact = must be ok. You need to test the normally CLOSED contact as well.
I have a wiring diag I will scan and post when I get to it in case it helps. Note is only for non SRT. They have a different config.