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Can anyone on this site provide a comprehensive list of conditions that prompt a Prius to demand the ever annoying IGN=10? :( And, better yet, can suggestions be provided to minimize or avoid each of those conditions? :)

First off, welcome to CleanMPG. IGN=10 is the value you will see when the engine is idling. In fact, it should be the only time you see IGN=10. If you see IGN=5, this is the indication that the engine has stopped.

Thanks for the welcome. Yes, indeed, IGN=10 demands that the engine idle - spending fuel while going nowhere. The Prius forces IGN=10 (idling) to heat or cool various components, or ...who knows what? If we know all the conditions causing IGN=10 to be imposed, we might be able to improve our overall MPG a little by avoiding at least some of them.

ICE will run if coolant temp drops to 63C(145.4F) until 73C(163.4F) is reached.

Therefore, avoid cooling the engine unnecessarily. Climate control, cold weather driving, etc. Block the grill in whole or in part, see recent thread on Winter Survival. In a long WS say down a mountain, the engine can cool enough to cause this. Its still better than everything else (nonEV) on the road.

You might find other tidbits in my Stages of Operation spreadsheet over at priuschat (in the knowledgebase)l. But I don't have anything comprehensive.

Thanks for your insight Ksstahead; I've seen your post on stages of operation and think it is really good.

But, in my case, both upper and lower grill blocks have been installed and I'm still seeing IGN=10 occuring when WTF is running in the mid to high 190s. I'm only guessing, but I suspect one of the conditions that might call for IGN=10 is a high temperature in the traction battery caused by extensive charging or discharging. I'm seeing IGN=10 in heavy stop-and-go traffic (when I use EV extensively) and just sit there watching all my care to build up a respectable MPG go down the drain while dealing with what appears to be a reversion to S1b. Nope, SoC isn't the reason either...I still see IGN=10 occur with 6 bars.

There must be more triggers for IGN=10 than low coolant temperature. Otherwise, my pet may just need an IT tune up ...maybe she's developing alzheimers and just forgets that we've already gone through the warmup stages. :biglol:

You might try PMing hobbit, diamondlarry, jimbok, efusco, etc with you observations, in case they have missed this thread. Several prius jockeys here really seem to know their stuff.