All,
I have VCDS but I'm a beginner using it. It's version 11.11.x, with a hex-usb ross-tech cable. My car is a 2011 A4. I'm not sure if what I'm looking for would be in a VCDS scan, and if yes, where. Here's what I did and what I'm looking for:

I'm in Colorado Springs, 6000+ feet elevation. The regular octane gas here is 85, premium is 91. I've always used 91, but on a road trip last week I had to get gas at a service station which was only selling 85 octane gas. The tank was near empty, and I filled up with 85 octane.

The car ran fine over the next 200 highway miles. I tried a few times accelerating hard, listening to hear if the car pinged or behaved badly. The car performed fine.

When I got near home I ran as hard a test as I could, putting the car in 2nd gear (manual transmission) at about 2000 rpm, flooring it and running all the way to the 7000 rpm redline. Again, I heard no pinging or knocking. There was no outward sign that I was using low octane gas.

I presume that the computer compensated, retarding the timing when I accelerated hard.

Now the question: Would that cause an event that I could see in a VCDS auto-scan? What would I be looking for?

 

log group 014 and 015. but why would you do that? that is only asking for problems. the engine uses at least 91 for a reason. 91 octane resists auto ignition more than 85. the ecu will try compensate by pulling ignition timing first, if it still sees knock or misfire, then it will start pulling fuel and reduce boost. you loose performance and efficiency and risk damage to your motor for trying such a thing.

 

Thanks!