Engine keeps starting and shutting down during traffic light stop

Is it anything like this: http://priuschat.com/index.php?showtopic=2...367185&st=0

I figure that if it's temperature related then these two threads might be related.

 

4 distinct possibilities, covered in the various theads linked, but not really summarized well....

1)In cold winter the most common cause of the rapid cycling of the ICE on and off, particularly just shortly after coming to a stop is that the battery SOC is high...this is common in the winter since the ICE runs more in order to keep/reach ideal ICE temp while driving. Thus, you come to a stop, the battery SOC is in the 'green' level and part of the 'job' of the car is to keep the battery SOC more toward the 'blue' zone. So, the ECU tells the car to spin up the ICE via MG1, it does so, runs briefly, then shuts off....each cycle puts a significant drain on the battery and once a more acceptible SOC is achieved the cycling stops (typically 4-7 cycles in fairly rapid succession).

2)ICE running to maintain it's own temp. In cold weather our little aluminum ICE cools quickly. Particularly at the start of a trip from a cold start the ICE might only reach 130 degrees or so before your first stop...it's warm enough to allow it to shut down as usual. But shortly after that it drops to 128 degrees due to radiant heat loss...the ECU doesn't like that an tells the ICE to warm back up. In this condition the ICE will usually run for longer periods of time (30-60 seconds?) and won't cycle back on quite as quickly once it shuts off again.

3)Low SOC....if you battery is drained a bit and you're running multiple accessories, esp. the AC/Defrost, etc. The ICE may spin up and run just to recharge the battery while you're stopped. This acts a bit more like #2 above where the ICE spins for relatively longer times and stays off for longer amounts of time.

4) I call this the 'tweener' state.... One of various conditions exist based upon ICE temp and battery SOC where the system thinks it can shut down, but as soon as it does the thresholds change and it triggers the start up code...I can't clearly say what these conditions are as I've only seen it a handful of times in the 3+ years with my Prius, so it's pretty uncommon, but definately occurs even with a warmed up vehicle. I think the car just can't see that it's cycling back and forth while it blindly follows it's algorhythms.

In no case are these situations of any concern.