OBDII Software

[MIPS]

Having borrowed my parents car all weekend I want to find out why the HELL it has such awful gas mileage and WHY the Money Light keeps turning on and off seemingly at random. There's a fault that keeps recurring and clearing and I don't own a scan tool for any modern vehicles.
The closest thing I got to a scantool is a very generic and unbranded OBDII to USB interface. I'm pretty sure it's just a level converter and an FTDI USB UART because it pops up as a COM port. So I guess I got the hardware but the software.....

I can google software and come up with countless software options that ALL demand money and include useless crippled or ad-ridden free versions or freeware where the money is in the tool they sell and the software only works with that but I don't really care for real-time performance data or sensor control or PID updates. The car is 15 years old and I just want to know what is setting the light and what faults are being stored.

Edited: actually it seems the adapter LOOKS like this one but god only knows if it's the same or a lookalike.