I have a scangauge II
Bought it to read faults off my car and van at the time.
Will only read fault codes off cars of year 2000 or newer so didnt work on my 1998 impreza.
The check engine liight came on my brothers 2002 Ford focus St170 while my dad was driving it a couple of times.
Used the scangauge and it gave a fault code which i then googled. The code it gave was the O2 or lambada sensor.
Only happens when my dad drives the car so my brother put it down to driving the car too slow
It can reset your check engine light once you have the code.
I may sell mine if i can get it back off my brother