Check Engine indicator

[Don9999]

My son bought a 1999 323i 2 weeks ago, and the check engine indicator came on within a few days. He used 87 octane fuel for his first fill-up, and noticed it was a little rough at low RPM. He used 91 octane for his second fill-up, and it is better.

Would the low octane fuel cause the check engine indicator? After driving about 100 miles on the second tank, the indicator has turned off. Is it true that the diagnostic code behind the indicator is lost?

Thank you for any help you can provide.

 

[Big Daddy]

No the code should still be there, the check engine lights reset after a period of time/mileage. I doubt the lower octane was the cause as the ECU should compensate for the low octane, however I would use 91 from here on out. Get a code reader and see what the light was for.

 

[Kirby]

Yes, read the code. My guess: F5 or F6 - Secondary Air System Low flow (but that's just a guess).