Guys, so I did my first service (1000km) today 

After a while, the technician gave me back my gaga and after all the payment is settled I drove the car away for about 200m when the check engine light is suddenly on ( never happened before )
So, I drove back to the service centre and let the technician try to resolve the issue.
And after about ~10 mins he return my car and the issue seems resolved.

So I drove the car away for about 100m only to find out the check engine light is on again    so, I had to drive back again to the service centre for the 3rd time in a day and this time the technician took about ~15mins before returning the car to me ( at this time, it's already 6pm )

The explanation he gave to me is that newer saga flx engine is different from the previous blm saga and it is build to comply with the European regulation so the engine sensor is a bit more sensitive than the previous engine model.
He said the problem was I'm using 2 different type of fuel ( petronas and shell ) and this causes confusion to the sensor. He further advise me to use only 1 type of fuel preferebly caltex or petron. 

The question is, is it bad to mix fuel from different brands because I read from google it's ok to mix fuel from different brands    my friend also mix fuel in his preve ( shell, petronas, bhp ) and there is no problem at all

This is only my first service and I had to return to the service centre 3 times in a day because of this check engine light problem    anybody here with saga flx encountered this problem before??
All sifus please help