I know I've seen this kind of information sprinkled through various threads, but I would love it if one of the "gurus" out there could summarize for me ALL the reasons why the ICE won't shut off; I think I must be missing something.

Lately it seems that there are more and more times when the ICE "should" shut off, but doesn't - instead it maintains an "idle" at around 1k rpm. Here are the parameters: engine is "warmed up" (known because ICE has shut off at least once since beginning of trip); no A/C (brrr) or defrost running; speed below 40 mph (usually about 38); flat road or slight downhill. I shift to "L" - car slows, but ICE doesn't shut off. OR, I "double tap" brakes (I know how to do this, most of the time it works), again, car slows (duh - I'm braking), but ICE doesn't shut off.

It has been getting colder around here, but I thought that once the engine and catalytic converter were warmed up on a drive, they would stay that way. I don't have the "nav" option, but I can also tell that my battery is not SO charged that the engine would run to avoid overcharging (BTW, I really don't get this - wouldn't shutting OFF the ICE, and running on EV, be the best way to run down the charge? So why won't it do that? Or does the "run to avoid overcharge" only happen when you are also braking?), because when I brake, I get some "recharge" on the meter. If the battery is fully charged (this often happens on one long, steep downhill in particular), the meter sits in the middle even when I'm braking. Also, I don't think the battery is too low, because usually I haven't been doing a lot of EV driving, or hard acceleration, just before.

I am usually coming off of a 40-50 mph stretch of mild hills (since that's what most of my driving consists of), where I've been trying to keep my rpms below 2K whenever possible, speeding down the hills and using the momentum to help me up (this is "DWL", right? or have I been using that term wrong - and doing it wrong?).

Lately (within the past two weeks - and it has been raining constantly and cooler), on some trips, after the ICE shuts down once or twice, it just refuses to do it any more! If I stop for a full minute or so, it might deign to stop, but the usual "double tap" and "shift to L" methods just DON'T work. So, What's UP?

 

With the colder temps and the rain lately, you are probably using the defroster more often, which runs the AC to remove the moisture. That will prevent the ICE from shutting down. The AC is the only thing that I know of that will just flat out prevent the ICE from shutting down at all.

 

She says she isn't using defroster.

As is my understanding, the ICE revving isn't done by fuel combustion, it's done by EV power running the ICE, which drains the EV battery back down to it's optimal programmed levels (around 50% charged). In other words, the battery is revving the engine to use up it's power.

I was quite surprised the other day when the engine came on at a stop light, after I got my car washed. (It's so pretty!)

However, I believe the reason why both my engine came on, and yours refuses to go off is the same reason. It's cold. There are parts which must be warm in order to be used properly, for the transfer between modes (ICE/EV/Hybrid/Recharge, etc.) to work without damaging any of the components, which are also warmed up when you start. After being wet, then being exposed to cool air, those "transfer" mechanisms cool off, and get too cold, which must be re-heated immediately, so the ICE comes on to do it.

I'm sure someone like Wayne can give a more thorough or technical explaination of exactly what's going on. Or call me wrong. Whatever.

 

Usually when the ICE won't shut off when you think there's no reason for it not to (everything is warm, battery is charged, etc.), it's because it's doing some self-maintenance or calibration. The system conditions itself, and at times needs to run the ICE for this.

It happens more often when the vehicle is new. If the ICE is hardly ever turning off when it should, then you might have a problem, but it's most likely just doing it's (good) thing.

 

If the catalyst is cold, it will run the ICE to bring it up to operating temp. Primary reason for running is to make sure the catalyst is at maximum efficiency -- minimum emissions.

 

I have noticed that the ICE in my '05 seems to run more in the cooler, wetter conditions than the '06 does. It's impossible to really quantify because obviously it would require identical driving styles at the exact same time.

I have wondered for a long time if there is some programming difference or some other improvement in the '06 that makes this the case.

 

I have noted the same behavior (ICE staying on) now that it has gotten colder and wetter. Sometimes it just refuses to go off under any circumstances unless one is stopped at a red light for 10-15 seconds. Based on my experience from last spring, this behavior is associated with the weather change. During the summer, it got much easier to keep the ICE off. My mileage has dropped by about 1 to 1.5 mpg since the summer (back to where it was during the spring).

I think the things people have mentioned here -- keeping components warm, self-calibration, etc -- play into it. I don't think there's anything wrong with the vehicle.

According to the Dearborn event thread, the engineers are saying there have been no updates to the code between '05 and '06 and they don't expect to ever need any. Perhaps there are other differences between the vehicles.

You mention your normal driving is hilly terrain at 40-50 mph. I have noted that those conditions yield excellent mileage in my truck (35 mpg or better) without the ICE ever turning off, and without trying too hard. Wondering what your experience is.

 

Yeah, I do get pretty good mileage under the cited conditions, as you say, without the ICE turning off. (Don't know if yours is AWD, but mine is, and I can get 35 on my afternoon commute, which is rolling hills and usually about 45 mph, with a few stretches of 35.) But suddenly I've been losing the extra boost I get when the speed drops and the ICE shuts off for a couple of miles through a small town.

More experimenting has revealed that it does seem to be cold/wet related. It was sunny yesterday morning, and after the normal warm up, shut downs began happening the way they used to.

Boy, is my mileage going to take a hit when the temp drops to the minuses! My last tank was below EPA avg. and it was only raining and 40 F.

 

Mine is 4wd like yours. Last winter, after my break-in period, I always got at least 28 mpg per tank, and usually at least 29 mpg, even in sub-freezing temperatures. I'm setting a goal of keeping things above 30 mpg at all times, now that I have more experience maximizing mpgs.

Since my driving is mixed town / suburbs / highway, with some pretty mileage-unfriendly stretches, my definition of success has been to stay above 30 mpgs at all times, and above 33 mpgs when I've had a mileage-friendly episode such as a long drive on rural roads on the tank. I started a tank at 37.1 mpg over 70 miles yesterday driving home from the mountains, but it will be a struggle to keep it above 32 mpgs by the time I hit 300 miles.

Every once in a while a really low mpg tank occurs, regardless of error. I attribute that phenomenon to self-calibration / battery reconditioning.

 

I drove the '05 for quite a while today and noticed some really interesting behavior.

My first trip was about a 11 mile ride and due to a motorcycle club get together every road in greater Boston was near gridlock. The '05 prettty much ran the entire time. It would go EV for short times but it wanted to run a lot. The few times it did shut off at lights it would start back up (ICE) as soon as I started moving. The temperature was about 65° today (snowed an inch yesterday) and it was sunny. It took an hour to go the 11 miles. No a/c, no lights, no vent fan and the average mile on the tank went from 29.9 to 30.0 mpg.

On the way home 6 hours later (about 45°, lights on), it would go into EV at every stop or at low speeds, stay in EV to 30-35 and the average mileage went from 30.0 to 30.3 in the 11 mile, 20 minute trip. Now the mileage meter was reset at the last fillup, 350 miles ago so it takes a lot to move it but it was really increasing quickly.

There are two things I am thinking on this. One is that since the car really hasn't gone anywhere lately so on the earlier trip it was conditioning the batteries or they really needed charging. The other is that there is some software quirk and needed to be rebooted. Had I thought of it during the first trip I would have shut down and restarted. Anyone had any luck rebooting? Anything change?

I am taking this car back this week while the '06 gets it's new bumper. My wife will drive the '06 for the next few months. Time to start observing, testing and experimenting on the '05.