Possible problem ahead?

You can try disconnecting the battery and letting the computers reset. That will force the computer to re-read your fuel level. There are many people, including myself, that has issues with the reading of the gas gauge in these cars. Sometimes I can put in 4 gallons and my car would fill up to full from only have 3 pips remaining.

 

how long have you owned it?

 

Prius is designed to use regular gas, so this suggestion seems odd. Maybe he had his reasons, but the full octane gas is not the key here. Rather, it is the Prius GenII gas tank bladder that is reluctant to expand fully in cold weather which causes many people trouble. Many threads here about the "Guess Gauge".

 

I've heard of high-octane gas causing the check engine light to come on in Prii. I don't know how the higher octane itself would have helped anything either. It was probably just a matter of allowing the fuel bladder to expand before adding more fuel.

Try only pumping gas at the slowest possible speed (first click on the pump handle). This helps the fuel bladder conform to the increasing fuel volume instead of shooting air up the fill tube right away, which causes the pump to click off.

What was the outside temperature? The fuel bladder is definitely less temperamental when it's warm.

I've heard of clogged evaporative components causing similar behavior. Maybe someone will chime in on that. A leaking fuel cap is also a common cause of the check-engine light.

The fuel gauges on these cars may have the most...personality of those in modern autos. They have some strange behavior. Sometimes, adding a few gallons doesn't cause the gauge to rise at all. Upon drawing fuel, the gauge readings are not linear (often, the first pip will last 80-100 miles, and the following ones drop off much faster).