3 quick beeps and engine shuts off

That's fairly similar situation that I regularly encounter here. There's a large shopping centre that I often go to, with a fairly large hill and a set of traffic lights about 500 meters before I get there. The hill is large enough that I normally get 8 green bars SOC and I often feel it reverting back to friction braking as I approach the lights. Similar to your situation, after the lights it's all low speed limit into the shopping centre and around their large car park. And just so annoying that I've got an overfull HV battery and the stupid engine wants to run continually. The situation is made worse by the fact that the car is not normally in "stage 4" at this point, so it won't drop back to EV mode by itself.

Oh well, at least there's something reassuring about knowing that someone else has the same problem.

BTW. When I first encountered this I assumed it was really battery temperature related, and that the charge to high SOC had simply caused the battery to get too warm. However I've since confirmed that it's not temperature related and that it really is due to high SOC.

The only explanation that I can think of that the software related to EV mode has like a general "battery in distress" override. So that basically any condition that puts the battery outside of normal operating parameters triggers EV denial. SOC too high just happens to be one of those conditions.

 

This is the conclusion in your last paragraph that I came to. My situation is the same with a set of lights over an old river bridge at the bottom of the hill. The engine is spinning while waiting at the lights using energy I could be using through the low speed section of town. I now resort to turning the car off until the lights change to save the energy.
I would have thought that EV in this situation would be encouraged rather than inhibited. I know I can drive for over a mile through the town without completely depleting the battery, and charge it back to 5 blue bars on the next down hill section. Total distance without using fuel and maintaining a good charge level would be over 4 miles.

John (Britprius)

 

Perhaps this is a difference in EU vs. US models. I see all green bars for 30 minutes as I descend a long winding mountain road, from 1000m to sea level. The engine stays off, or spins at 1000RPM if above 42 MPH, and 99.9 MPG shows on the MFD. I watch as the battery temp climbs to 49C after the SOC goes as high as it will. All braking at that point is via friction, with some engine braking coming on at higher speeds, but that does not consume fuel. As soon as I encounter the next upslope, the engine kicks back in as expected, but not before.

The only times I see the engine stay on when it seems like it should shut off is when it is not hot enough, and tries to get up to preferred heat again. In this hot climate, that is not often.

 

i always saw my engine come on, on a warm day after driving on the highway and coming off to a 20mph road, with full green bars, the car would not go into ev. this was a regular part of my commute.

 

Hi nh7o. I think there is some confusion in that myself and Britprius were referring specifically to EV Button activated EV mode, and not to full electric mode in general. The UK and Australian model gen2 Prius have the EV button installed as standard equipment.

Many of the conditions that inhibit EV Button activated EV mode do not seem to affect regular full electric mode operation (well some of them do to some extent, but it's more like a suggestion to use EV less freely rather than an outright denial as in the case of the EV button).

In the case I described above the high SOC simply inhibits me activating the EV button to lock it into EV mode for the low speed driving on level ground that I'm doing at that point. After my initial acceleration from the lights regular full electric mode *would* actually work *if* the car was in "stage 4" hybrid mode. However I'm typically in "stage 3" at that point (up to temperature but haven't done the ten second idle then engine cut out dance). So after I accelerate from the lights the engine stays on for the remained of my journey, which is approx 1 km at low speed.

BTW. This is doubly frustrating to me as I then have to park the car in the hot sun with full 8 bars SOC, something that can potentially overheat the battery. So after being denied EV operation for that last km I often park and then have to sit there wasting time and energy by running the aircon at full blast and waiting until it drops to 7 bars before going shopping or whatever.

 

There are a number of possible factors involved there bisco. It may be temperature or SOC related, but at 20 MPH it may simply be that you're stuck in dreaded "stage 3" hybrid mode where the engine continues to run regardless.

 

Just out of interest nh7o, have you ever tried activating "B" mode nice and early (while the SOC is still normal) on this particular decent. I'm just wondering if the delay in reaching full SOC and the greater energy dumping would have any measurable effect on the peak battery temperature.

 

Yes, when I got Priidash going, I experimented with this and I found, counter-intuitively, that B mode with batteries less than full will still allow battery charging at close to the same level as without B mode. In fact I don't bother with B mode much anymore on the long descent, as it does not prevent the batteries from reaching the charge level that causes the thermal rise, and I don't like to hear the engine wind up to such high RPMs. As the battery reaches full there is a reduced RPM B mode that is automatically turned on by the HV ECU, and that is easier on the ears and only requires a bit more friction braking. I know for sure that I won't be getting the Prius typical 100K mile life on my brake pads.

 

congrats!

 

Yeah, it probably had a "floating" signal, so that a bit of electrical noise could trigger it at random. That makes sense now.

If you ever wanted the EV modification you could probably just reconnect it (properly) and it would work.