I have also had an alarm after ~3 Minutes. I checked the coolant, engine oil, hydraulic fluid, and even threw an ODBII reader on it to see if I could get a diagnosis all to no results... everything looked good. So I googled the problem, got brought here, read the thread RE Scavenger Pump Sensor, and promptly ordered one. I went to install it today and found the 1st oil pressure sensor near the Battery Box but had read somewhere to lay down and look behind the battery box. To my surprise behind the battery box, I found an oil filter that had unscrewed from the tractor. I had the tractor recently serviced, I guess the tech was a little light with "hand tighten". My guess is that after some point (3 minutes for me) the tractor gets to the point where it needs oil filtered and when it kicks on the pump and then the sensor goes... "no, there's an issue" and kicks off the pump and kicks on the alarm.
So... STEP 1: Check all fluids AND filters... then everything else on the thread.