OBD II cheating (NAC)?

[tihol_tiholov at sd27.bc.ca]

Hi all, I have 2 questions:
Car is 1999 VW New Beetle, 137,000 km, running fine, good gas milage.

1. Is there any way to turn off the Check Engine light without the VAG
tool?  Suspect that poor/funny gas was the cause, since at one point last
week the light did go off on its own for a day, then stayed on again.  The
car has had a lot of different gas put in it and it is driven more than 200
kms daily.   Did the 10 minute battery disconnect to no avail.  When I
start the car, Check Engine light goes off for a split second and then
again goes on.
2. What does "graded" or "non-graded" gas means?  The Check Engine light
stayed on for the first time when filled with gas referred to by the gas
station person as "non-graded".  It was regular gas, 87 octane.

As always, appreciate any input and TIA

Greetings,
Tihol