Occasionally, I can't get my TCH to switch to EV mode. Sometimes on the freeway in rush hour, I slow down to under 40 mph and the car will not switch to EV mode. This is usually when I have been driving in mostly EV mode for a couple of miles and I have to speed up, then the engine comes on. Then when I slow down, (foot off the gas) the engine stays on. This usually happens when the battery is near full as well! I would think it would be more likely to switch back to EV mode with the battery full. If I come to a complete stop for a few seconds it goes back to EV mode Does it overheat or something after a few miles in EV mode? Does this happen to anyone else??

wes878, your TCH was in stage 3. Stage 3 is when the TCH is warmed up, and as you coast down under 40 miles per hour the ICE stops. Stage 3 allows you to continue in EV mode until low SOC or acceleration restarts the ICE. Once restarted the ICE will run until you once again coast down under 40 miles per hour (coasting between 35 and 40mph enters stage 3)

Stage 4 is full hybrid mode. The only way I know of to enter stage 4 is to come to a stop for 7 to 10 seconds after the TCH is warmed up. Once in stage 4, anytime the SOC shows over 2 bars and you coast at any speed under 40mph, the ICE stops in 2 or 3 seconds. I've also entered stage 4 without a full stop, but was just barely creeping along at 2 or 3 miles per hour.

I believe stage 1 is the initial minute or so after the ICE first starts when the timing is retarded to rapidly heat up the cat converter. The ICE will shut off if you stop during stage 1. Stage 2 is the final warmup phase, and ICE will not stop until the coolant temps reach normal operating temperatures. This appears to be a little while after the temp gauge has reached it's normal reading.

Another behavior I have observed when stopping at a store for a short time, the TCH will go from stage 1 directly to stage 4 if I am slowly (5 to 15 miles per hour) driving or coasting after about 30 seconds.

Thats the thing, I am coasting to under 40 mph, and the EV mode does not come back on sometimes. I have a full or almost full battery, and the road is slightly downhill. These seem like optimal conditions!

Sometimes the TCH will not go into EV. Could be coolant or cat converter temps dropped too low. Could be the traction battery is hot or cold.

Are you using the ECO button? Many of us have noticed the TCH goes in to EV mode more frequently with ECO than without. ECO tells the TCH the priority is MPG not cabin temperature comfort.

I stongly suspect the cat converter temperature is the reason. I have a long, gradual downhill just before turning onto my home street that I always take in EV only or fuel cut, depending on speed. I have noticed that the engine will not always shut down when I slow to make the turn. I have also tried to put the car in neutral for the downhill stretch, and even that will not shut down the ICE immediately. But it does eventually shut down.

It is the ignorant among us that will eventually destroy us all.

This thread caught my eye in the new FAQ and I thought I would bring it back for a comment.

I too have experienced times when the car will not go into EV mode when it really seems like it should. Like FastMover I too have a long downhill stretch to my home that I ususally take in EV mode. But sometimes the ICE stays on all the way home. One time when I got home I sat in the garage and let it idle, waiting for the ICE to kick off but after 7 minutes I got tired of waiting and turned the car off. Had full battery, just got off the highway after 23 mile drive at 40MPH avg speed with occasional use of EV in stop and go traffic, 45F outside temp, ECO on, environmental controls set to Off and the ICE still would not turn off. What else could it be?

One thing for sure. If you slip it into Neutral and it stays running. That tells you it's not any upgrade your driving on. The only two things left are the catalytic converter or the traction battery is low.

A guess, since I'm far from an expert.
To get it into full EV mode, you need to stop (in gear) for approx. 8 seconds once the engine is warmed up (needle half way) and listen to (or watch the screen) the engine. If it turns off after one second, you are not in full EV mode. If it turns off after 5-7 seconds, you are in full EV mode. It's possible your highway drive was started before you achieved full EV mode. The short stop and starts didn't allow enough time for it to get into full EV mode.
As to sitting in your driveway, I can't answer.

If you in the EV mode for a few miles and the temperature is cool. The catalytic muffler might have cooled off. But with the ice on it should not take but a minute to heat it back up. I thought maybe a few bad cells in the traction battery. But you drive in the EV mode for a few miles which is the same as i'm getting.

How is your gas mileage on each tank. Is it as you expected.

I keep forgetting to say your heater or AC turned on could have something to do with the ice running a while. If this happens again be sure to press the off button on the AC/heater. Then see if it has any effect.

I don't let my engine idle at all except for a minute or so at a red light. If it does at home I shut it off. I do run in the EV mode mile to our house in the country. The ice kicks on usually a few hundred feet from the house. It continued to run till I shut it off in the carport. I know the reason it run, the traction batteries are down to 40% discharge. They charge back up in the first two miles of driving the next day.

You might want to have your traction battery and ECU checked out just to make sure all is ok. It should be in warranty but that depends on your cars miles.