[rdalemercer]

Since the Hybrid Synergy Drive that the CT200h uses is essentially the same as the Gen3 Prius, this may shed some light on how the synergy drive provides instructions to enter (or make available) the EV mode. This is not my information -- and I wish I could give attribution to the OP, but it's been a while since I copied this to my HD so I wouldn't lose it.
The Stages:
S0:

• From power on until the ICE starting for warming up (approx 12 seconds)
• You can enable the EV-Drive Mode during this S0, if the conditions are allowed so (refer to your owner's manual)
• The EV-Drive Mode can not be entered when:
  • (1)the temperature of the hybrid system is high (ie; the hybrid battery is above 46C),
  • (2)the temperature of the hybrid system is low (ie; the hybrid battery is below 0C),
  • (3)the hybrid battery charge level is low (three bars or less),
  • (4)the windshield defogger is in use or
  • (5)the engine coolant temperature is below 0C (maybe 20C on the US Prius)

S1a:

• When the start coolant temperature is below 40C, the warming up starts and continues for approx 50 seconds after S0.
• You cannot enable the EV-Drive Mode during this S1a.
• The ignition timing is very late, after the top dead center - therefore the engine does not have enough power to drive Prius or charge battery. Basically, Prius cannot use the engine power when you drive.
• Prius is driven by battery power and the battery is discharged.
• It is a good idea to drive slowly or stand still warming up in this stage.
• When the start coolant temperature is between 41C and 60C, Prius is in this stage, but the engine does not start automatically.
• When you press the accelerator (including driving), the engine starts and runs for approx 50 seconds or until the coolant temperature reaches 65C, the ignition timing is very late too.

S1b:

• This is an extended warming up stage.
• You also cannot enable the EV-Drive Mode during this S1b on Gen3.
• The ignition timing is now normal, and the engine is able to provide power and charge battery.
• You are now ready to drive without any penalty of battery discharging.
  • (A) if the coolant temperature is still below 40C after S1a, the warming up continues until 40C.
  • (B) if the coolant temperature is between 40C and 50C after S1a, the warming up continues until 50C.
  • (C) if the coolant temperature is between 50C and 60C after S1a, the warming up continues until 65C.

S2:

• Following S1a or S1b, Prius goes to this stage.
• Prius acts normal until the coolant temperature becomes 70C (going to S3).
• The EV mode speed is limited below 10 mph on the NA Prius.

S3:

• When coolant temperature becomes above 70C, Prius goes to this stage.
• Prius acts normal, but Prius requires an "idling check ceremony".
• The EV mode speed is now allowed up to 25 mph on the NA Prius.
• The "idling check ceremony" is done during an accelerator off gliding for several seconds on Gen3. (on Gen2, Prius needs a complete stop or very slow walking speed for the ceremony)
• The engine continues to run for several seconds during the ceremony.
• After the ceremony, Prius goes to the S4.

S4:

• Prius now completed the warming up stages and in a full normal condition.
• If the coolant temperature is above 60C on power up, Prius is already in this stage.

If someone has newer (specifically for the CT) information, please post it.

 

[Sleepypete]

Wow - very interesting, explains a few things too like "why is the car driving on battery when the battery is low ?" when I'm just starting up in the morning or when coming home from work.

Another cold temp observation :
I've noticed that the power steering offers no assistance when the car is very cold, probably in the S1a stage. It feels like having 2 flat front tyres. Good to have an idea why Gorilla Arms might be needed to take the car out of a parking spot when it's cold . Could be a "I'll give you enough battery juice for the motor but not for the power steering".

 

[gpunkt]

2010 Prius and 2011 CT200h behave alike, or if I may say: dead even.