Engine "Run-on"

Long answer: Look for the 4 stages of prius operation in this forum. Your probably not in stage 4.

short answer: your engine isn't warm enough.

 

splendid,

More than likely, short periods of "run on" are normal.

I can think of three situations when it is typical:
* The ICE, Internal Combustion Engine, is running to warm up
itself and/or the catalytic converter.
* The ICE is turning MG1, Motor/Generator1, as a generator to bring
the SOC, State of Charge, of the High Voltage/Traction battery up to
the level that the HSD, Hybrid Synergy Drive, computers try to
achieve/keep in cold weather.
* The HSD is rotating and slowing the ICE so that it can be stopped in
EXACTLY the right location so that it can be restarted most easily and
with the minimum jerking or stuttering.

The SOC level noted above is somewhat higher than in warm weather.
It has been speculated that as getting and maintaining this level
requires that more electricity flow into and out of the HV battery, it's
purpose is to warm up the HV battery due heat generated by the
reversible chemical to electrical conversion process in the battery.

As long as you aren't seeing any warning lights, hearing any horrible
noises, or feeling any really extreme shudders, etc on restart, I'd say
there's nothing to worry about.

I hope this helps.

 

If you mean very brief turning over of the engine, it is normal. The engine will attempt to stop at a specific crankshaft angle. When cold, and/or when the oil is too thick (ie not 5W30) it will sometimes fail, and will retry until successful. It sounds like run-on, but it isn't. The engine is being spun by MG1, not burning fuel and sputtering.

-Usually- this behavior will stop once you get a year or two of use on the car. But apparently, not always.