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This information is adapted from information published on the Prius Warm Up Stages. Our cars operate much the same. This information should help us all understand the cars better and get better gas mileage. Over time I will edit this post as I learn more about how the FFH works. Stage 0 (S0): Car begins in EV mode. Certain HVAC settings may cause the ICE to immediately start instead of allowing EV operation. The FFH will stay in S0 until the power demand from your acceleration exceeds the power that can be provided by the HVB and the electric motor. Stage 1a (S1a): Initial warm-up with late ignition timing and diminished engine power. Engine-off at stops: No. Engine-off gliding: No. EV Mode: No. Unless the ICE is already quite warm (above 60 or 65 C it appears), S1a begins at the conclusion of S0. S1a terminates at about 40C coolant temp. You can tell when S1a ends because the ICE begins providing the power needed to propel the car and charge the battery. S1a is the worst stage because the ICE is on, burning lots of fuel to warm itself up, and the electric motor is powering the car and depleting the battery. One should drive slowly or sit and charge the battery during S1a for optimal fuel economy. This is why some users (rjent & others) reported better fuel economy on short trips using remote start to idle the FFH until S1a finished. During S1a, the ignition timing is retarded & the ICE is producing almost no power. The focus is on heating up the catalytic converter as quickly as possible. After my driving last night it appears that the car will go into S1a after S0 even when the coolant temp is above 40 C. Last night I got in the car after an errand and the coolant temp according to ET Mode was 57 C when I started the car. The car went into S1a after S0 and stayed in S1a until the coolant temp reached 65 C. Once the coolant temp reached 65 C it went right into S2. Tip: You can skip S1a and go right to S1b by briefly shifting the car from D into L and then shifting back to D. You must wait until S1a starts to do this and you must keep the shifter in L until you hear the engine sound change indicating that the car has gone into Stage 1b. It is unknown what impact this might have on the life of the ICE or wear and tear on it. Ford has informed us that we will not cause permanent damage by doing this. You can tell if the car is in S1a or S1b by the sound of the ICE when accelerating. In S1a the ICE will continue at idle and not rev while accelerating. However, it is a little harder to tell when stopped idling if you're in S1a or S1b just by the sound. The way to tell is to look at the Engage screen. The Engage screen shows total power demand placed on the ICE for both driving the car and power to recharge the HVB. When in S1a the power demand on the ICE at idle is less than .5 bars. When the car transitions to S1b the power demand will jump to typically about 1 bar while at idle. Since S0 & S1a typically deplete the battery, the ICE begins rapidly charging the battery once entering S1b. Stage 1b (S1b): Continued warm-up with normal ignition timing and power. Engine-off at stops: No. Engine-off gliding: No. EV Mode: No. S1b is much better than S1a because the engine will power the car and the generator normally, but it still cannot engine-off glide. This stage immediately follows S0 if the coolant temperature is high enough.. Otherwise, S1b begins when S1a ends and lasts until the following points depending on engine coolant temperature at the start of S1b: below 40C/104F: until 40C/104F.between 40C/104F and 50C/122F: until 50C/122F. (I verified this last night)between 50C/122F and 60C/140F: until 65C/149F. (I verified this last night)I need to verify the numbers above in ET Mode but this appears to be what I have approximately experienced.Post PCM update (13B07) it appears that S1b ends following the table below below 40C/104F: until 40C/104F.between 40C/104F and 45C/113F: until 45C/113F.between 45C/122F and 55C/140F: until 55C/131F. The coolant temp can also now drop as low as 51C/124F before making the ICE run for heatStage 2 (S2): Full Operation Engine-off at stops: Yes. Engine-off gliding: Yes. EV Mode: Yes. This stage starts when S1b ends. If the ICE temp falls below 50C you will go back into S1b. In the winter, the car spends a lot of time going back and forth between S2 and S1b in city driving. Notes on HVAC usage If you have the heat turned on, then the car will not move from S1b into S2 until the coolant temp reaches 60C. Heat use also makes the car much more likely to switch back into S1b after having been in S2. Note: Engine-off at stops and Engine-off gliding will not work while the window defogger is on, even if in a stage where they otherwise would work. Read about the Prius Warm Up Stages at: http://priuschat.com/threads/gen3-warming-up-stages.76501/#post-1068435