About 25% of the time, my TCH NEVER goes into EV mode. All of the conditions are right for it (warmed up, below 40MPH, light on the gas , etc.) but it refuses to do it. I find that when I stop, restart the car, it then goes into EV mode as expected. Anyone else have this problem and if so did you find a solution? My guess is that the catalytic convertor heat sensor is faulty and during these no EV times, just never lets the system know it's at the proper temp. When I go in for my 5000 mile checkup, I'll have the dealer look into this.

 

Is your battery drained? Had to ask since u did not mention it. Mine does not go into EV sometimes too.

 

Probably because the car is making MORE decisions than you are.
Here is a snippet from priuschat.com that explains the various phases of EV and Super-EV (Golfcart) mode. An interesting read if you take the time. Notice how many different stages there are. Not just EV Mode/Non-EV Mode. This is a Prius dissertation but it applies in large part to the TCH.
The Five Stages of Prius Hybrid Operation
The computer that controls the operation of the Prius hybrid system (HSD) appears to have 5 distinct stages of operation, which I will call Stage 1, Stage 2, Stage 3a, Stage 3b, and Stage 4. (Abbreviated S1, S2, S3a, S3b, S4.) Briefly, they govern how the HSD will combine power from the Internal Combustion Engine (ICE) and to and from the battery via two motor-generators, MG1 and MG2. The following was drawn principally from my observation, after reading several posts on the subject. EV (electric vehicle) mode is distinct. I drive a 2004 "package AM" Prius.

Disclaimer (from the author of this article): I am not an engineer or a technician. My understanding of this is not complete.

Definitions:

ICE:
The internal-combustion engine.

SOC:
The state of charge of the battery. (How much charge it has.) Shown by an icon with 8 bars on the MFD (multi-function display).

MG1:
Motor/generator 1. Most commonly used to crank the ICE for starting, and to generate electricity from the output of the ICE, which can then help drive MG2 or charge the battery.

MG2:
Motor/generator 2. Most commonly used to drive the car, alone or in combination with the ICE, and to provide regenerative braking.
(Occasionally MG1 and MG2 can act in arcane ways as well.)

Golf-Cart Mode or stealth mode:
(so called because the car is as quiet as a golf-cart) is my term for when the car is moving on electric power alone, with the ICE not running. Some have used the term “stealth” which I think sounds too militaristic for such a peaceful car, and is misleading because the car is not completely silent when moving on electric power. There is the whirr of the motor, and the crunch of tires on pavement.

EV Mode:
EV Mode is when Golf-Cart mode is entered via an EV button or switch. The button is standard on European and Japanese Prius. The button or a switch can be installed on North American Prius. For DIY instructions, see Dr. Evan Fusco's article in the Knowledge Base. For a relatively easy-to-install kit, visit Costal Tech
You cannot enter EV mode if: You are in S1; your SOC is very near or below 3 bars; you are accelerating; your battery is too hot; or you are moving at 34 mph or faster. EV mode will automatically disengage when: your SOC reaches 2 bars; you step too hard on the accelerator; you reach 34 mph; or your battery gets too hot. The upper limits of speed and acceleration, and possibly the lower limit of battery SOC are different for EV mode than when Golf-Cart Mode is chosen by the computer. In EV Mode the upper limit of speed is lower, but the permitted acceleration is greater.
Normal Mode: Any time the car is not in EV Mode. In Normal Mode, the car may go in and out of Golf-Cart Mode.
I have seen references that say the transitions mentioned below depend on coolant temperature. I have also seen references to the importance that HSD gives to keeping the catalytic converter warm, to reduce emissions. I will simply refer to the system temperature in the discussion that follows.

The Stages:

S1:
In Stage 1 the ICE is cold. If not prevented by use of the EV switch, the ICE will start a few seconds after the car is powered On. Until the system reaches the S1/S2 transition temperature, the ICE will run continuously. This accounts for the anomalous observation of electric regeneration or no arrows (coasting) at the same time as a low instantaneous mpg reading. No power is being drawn from the ICE, but it is running. Also in Stage 1 you will notice that battery power is used for even mild acceleration. In Stage 1 the HSD prefers not to draw power from the ICE if it is not necessary. You cannot enter EV mode while in Stage 1.

S2:
When the system temperature reaches 40 degrees C. (104 F.) the computer goes to Stage 2 operation. The original Japanese poster gave more detail than I clearly remember, but it appears that in Stage 2 the ICE will shut off if it is not needed to provide power. At a stoplight, in S2, the ICE will stop immediately and fairly smoothly. However, the car will not go into golf-cart mode in Stage 2. It can draw power from the battery or it can recharge the battery, but will not use the battery without the ICE. I have not ascertained if you can enter EV mode from S2.

S3:
When the system temperature reaches 73 C. (163.4 F.) the computer goes into Stage 3a. In S3a the ICE will not shut off unless you come to a full stop for 5 or 10 seconds. Paradoxically, it is more reluctant to shut off than it was in S2, and in S3a it shuts off very roughly. You will feel the car shudder. But once it does shut off at a full stop in S3a, it will then be in Stage 4 operation.
Once the car is in S3a, if you reach 34 mph without having come to a full stop for 5 or 10 seconds, the car will go into S3b operation. S3b is identical to Stage 4, except that if you slow down below 34 mph and apply the brakes, you will be back in S3a. In S3 you can engage EV mode providing that you meet all the conditions for EV mode.
I have observed that at the full stop in S3a sometimes the ICE stops after 5 seconds, and other times runs for 10 seconds before stopping. I do not know what determines the difference. I have also observed more than one rough shut-down in a trip, suggesting to me that perhaps the ICE may sometimes stop roughly in S2, and may not stop immediately when you let off the accelerator in S2. I repeat that I do not clearly understand Stage 2 operation.
Coming to a full stop while in EV mode does not seem to trigger S4. You must be in normal mode when you stop in order to enter S4 operation.

S4:
Stage 4 is normal, full hybrid operation. The Prius is most efficient in S4. The car will go into golf-cart mode at the computer’s discretion. You can encourage it to do so by lifting your foot off the accelerator pedal for a moment, and then pressing on the pedal very lightly. This is known as “feathering” the pedal. Feathering does not force the car into golf-cart mode, nor is it necessary for the car to go into golf-cart mode. It merely encourages the car to do so a little bit sooner than it would otherwise do on its own. The benefit of feathering the pedal is questionable, since the computer is deciding when it thinks Golf-Cart Mode is most desirable. Increasing the time spent in Golf-Cart Mode may only increase the efficiency losses involved in charging the battery and drawing power from it. On the other hand, encouraging Golf-Cart Mode when the SOC is very high may be useful, as it creates head room in the battery to accept charge wheen needed.
Above 42 mph the ICE must spin, and will generally provide power. It is possible for the ICE to spin without providing power to the car above 42 mph, and this has been observed. But since the ICE is more efficient at these higher speeds, Golf-Cart Mode above 42 mph (Super Golf-Cart Mode) is unusual. So the maximum speed in EV Mode is 34 mph, cutting out at a tiny fraction over 34 mph, and the maximum common speed in golf-cart mode is 42 mph. You can go faster in non-EV golf-cart mode than you can in EV mode.
Thanks to jfschultz for providing the transition temperatures given above. They were cited by a Japanese poster some time ago but I had forgotten them.


Bron: PriusChat.com

 

Great Info!!!!!!!!!!

 

This problem occurs even with the battery at 90%, engine warmed up (15 min), below 40MPH and the usual gas pedal techniques. The other 75 % of the time it goes into EV easily, I can tell right away that it is in this "No way you are getting EV" mode

 

I have had that happen, and it is very puzzling.

I have wondered what a plug-in kit would do for our cars if they don't reprogram the locic to run the battery down more. I have parked more than a few times with only one bar missing from the battery meter. If the battery was that full with a larger battery and a plug-in feature, I could not fill much from the power grid.

 

I have seen this problem with same conditions, a few times. No matter what, the car just refuse go to EV mode, even in the 25 mile speed zone. This is what I have found to work: I just park my car to the side for about a minute or so, then after about a minute it goes to EV while parked. Now I can go on driving in EV and it works just fine... very puzzling. One think I observed though is that, this happens mostely when the pattery is almost full, just one bar short of full..

 

I think you're trying to outguess the computer on what mode the car is using to drive the wheels. I got my TCH in September and after driving myself nutty watching the gauge which shows whether I'm EV or gas mode, I now let the computer decide. I average 37.5 to 39 mpg per tankfull without angst. I love my TCH