Why is my engine running????

[eggehad]

Ok, all you 2006 HH gurus out there:
I was getting between 30-32 MPG up until about a week ago. Now all of a sudden, It has dropped to approx 26 MPG, and I have traced it to my engine running when it didn't before:

1. Battery charge is green
2. A/C & Heat are OFF
3. Car is in Drive, foot OFF gas pedal, Coasting down hill (regen braking is active)
4. Engine is HOT (has been running > 30 mins)

I can stop the car, on the hill, and the engine continues running. It DOES NOT SHOW on the onscreen monitor as running, but it is idling along. It does NOT turn off if I just sit there, (ok, I've never sat there for very long, so it probably would eventually). If I shift into park, then back into drive, it WILL turn off the engine.

Couple of other things which might be relevant
1. The regen braking seems to be also acting up (the engine compression was used yesterday to slow the car, instead of regen braking!). I shifted into park, and that too started to work again. Battery wasn't fully charged!
2. This all started on or about the time I installed the SoundLinQ SLI into the cars AV network (I don't see how this could affect it, but it is the only mod I've done in the last week)
3. I drove up Fremont Peak last weekend (when I really noticed this very annoying behaviour described above). I noticed that when the engine runs, while going UP the hill, it charges the battery at max charging rate. One you are at the top of the hill, guess what? The battery charge is green- just in time for you to go DOWNHILL. So of course, I tried to creep up the hill (at like 5MPH) to keep the engine off. No go. My car would NOT let me do that. So all the way down the hill I got to burn my brakes, and it used engine compression braking then (the first time I noticed it) too... So annoying to drop a couple thousand feet in only a few miles while only getting 20-30 MPG while doing it. Adaptive engine algorithms? I've been at war with my car ever since this trip, trying to get it to keep the engine off- so far, I'm losing the battle. If I've got to pull over in heavy traffic, to switch from park to drive again, I'm just going to scream!

(Does anybody know how to force the engine OFF manually, so I can get the battery charge level low enough, that I might get even a little benefit from the downhill?)

/ONSOAPBOX/
Really steep hills are a problem for the HH. From my experiences so far, the hybrid offers absolutely NO advantage to anybody who drives in very hilly terrain... Toyota hybrid control algorithms are sorely lacking, at the very least, in this case....
/OFFSOAPBOX/

Any ideas? I'd love it if anybody could shed light on when the engine runs and when it doesn't (and why!). I'm in the mountains a lot, so this is a pretty important topic for me...
Thanks!

[Tideland Prius]

wow.. there's a perfect example of the EV Drive mode in the Prius heh.. drive around, drain the battery then recharge down the hill.

Anyway, hmm... I was gonna say battery at 8 bars but you said it wasn't at 8 bars when it displayed this behaviour or was it only for one particular instance?

cause the engine will run and "drain" the battery if it's too full.

Also, going up the hill, my Prius doesn't charge the battery. It has the arrows from the engine to the wheels and the engine to the motor to the wheels. Nothing is going from the battery or to the battery so your SOC shouldn't be affected.

All I can think of is maybe run your A/C. Is the HiHy's A/C electric? If so, run the A/C so that it'll use up the battery so the engine doesn't have to drain it.

[eggehad]

Thanks for the reply. I don't see how the gas engine can "reduce" charge on the main battery - but then I realize I really don't have any detailed idea of how the hybrid system actually works. I'd like to monitor the current to/from the main battery myself, but I haven't actually figured out how to do that. I've done it with the aux battery, but that says very little- since the current drain is negative (few amps) when the inverter is on..

I originally assumed that the cooling radiator (in the driver wheel well) and the cooling fluid (pink) which cools the electronics, actually dissipated the heat of the PWM braking system when the battery was charged. Experiments since have dispelled that notion, since I've realized that the cooling system can't dissipate much power, and a "fully" charged battery, invariably just disables regen braking. Thus, we ride our brakes, and they dissipate the heat themselves when the battery is full.

There seems to be a couple of possibilities to monitor what is actually going on, the OBCD2? port, and/or modifying the system with some electronics to actually monitor the charge of the battery myself. I lean toward doing it myself, but I need some technical docs before I do it. So far, I haven't been able to convince myself that I want to part with $700 to get the service manuals, so I haven't....

I'll try some experiments with hall effect sensors, and see if I can get an accurate current from the HV cables during operation. I'll probably watch the current profile, and log it on my laptop- but I won't have a way to synchronize that with what the car is actually doing-
So I'm not sure how useful my data will turn out to be.. Has anybody else done this before?

In any case, THANKS! for the suggestion, I'll add the A/C degree of freedom to my testing as well, to see if I can find a pattern there.

[Tideland Prius]

whew... I'm not as electrically intelligent as you may think heh.

All I know is that the engine can sort of...hmm.. can't find the term at the moment but basically discharge the battery since the computer is designed to keep the SOC at a certain level (60% on the Prius).

Hmm... have you tried a ScanGauge? Can-View has one for the Prius, they may have one for the HiHy.