Engine keep running but not shown on screen

Maybe, maybe not. How long did you stop for in traffic. Usually the engine will cut out (prius enters hybrid stage 4) after 10 seconds or less of idling. Sometimes however mine takes a little longer, occasionally up to about 17 to 20 seconds in very humid rainy weather.

Driving at 30MPH in stage 3 it is completely normal for the engine to always remain on (unfortunately).

Stages of hybrid operation: http://www.techno-fandom.org/~hobbit/cars/five-stages.txt

 

>12.7V >12.5V 13.8-14.2V

For anything less than 12.5V sitting voltage, you should charge your battery back up to full (13.2V).

 

Hi Allen. It's best to test after the car has been completely shut down for several hours at least.

Many people get less than 12.5 volts with the prius off, and the exact value will depend upon how you measure it. For example I can measure anywhere between 12.3 and 12.6 depending on whether I use the MFD service menu or a voltmeter. The difference is not so much the accuracy of the measurement system, but more about the differing battery loading in each case. If using a voltmeter you get maximum reading with the prius completely off (smartkey out of range) and if you wait about 5 minutes after popping the hood, have all doors and hatch closed, and don't touch anything for that five minutes. You have to do this to make the ECUs sleep. So you see it's not as simple as just saying >12.5 volts.

 

Those non-running numbers look too high to me, at least on a Prius.

My 2012 Prius manual, p. 567, says:

12-volt battery
Open voltage at 68F (20C)
12.6 - 12.8 V Fully Charged
12.2 - 12.4 V Half Charged
11.5 - 11.9 V Discharged
(Voltage is checked 20 minutes after the hybrid system and all lights are turned off.)

Past battery checks found mine to typically be half charged.

 

Yes, but were your past checks performed with the battery truly open circuit? If the battery was still in the car (and connected) then those figures are not necessarily applicable. That's the whole point I was trying to make with my previous post. Voltage measurements depend not only on the state of charge, but also on loading (current) and recent loading history.

 

I'm checking with an external DMM, after the car sits off for an hour to all night. The MFD voltmeter available on the GenII is absent from my GenIII. The other connected parasitic loads should be similar in scale to the battery's own self discharge, so should have little impact on the reading.

 

No that's not the case, at least it's not the case with the gen2. When you open the door to pop the hood, or if you open the hatch to access the battery directly, then a bunch of ECUs get powered up in preparation for the car being driven. On my prius this is enough to drop the battery voltage from about 12.6 to 12.7 down to around 12.3 volts.

If you then close all the doors and hatch (it's ok to leave the hood open) and wait several minutes, then you'll hear a relay click off and the ecu loading is removed or reduced, and then the battery voltage starts recovering back to it's true open circuit voltage (about 12.6 to 12.7 for mine).

 

All sounds good except for the last measurement.

Are all the doors and hatch closed at this point? Leave everything closed and come back and measure again in a few minutes after the ECU's have timed out and gone back to sleep.

Even if your battery is slightly weak I don't think it's at the point where it should cause any driving anomalies.

Try you're engine cutout test again. Try turning the aircon off for a minute and see if that allows the engine to cut out (after it's warmed up).

 

Like I keep saying, you've got to wait a few minutes *after* all the doors are closed before all the ECUs go to sleep, only then do you get a true (or at least near) open circuit voltage. If you stand by the engine bay you'll hear a relay click off after a few minutes, and then the battery voltage will start rising.

 

Not on a good AGM battery, and I was being conservative. The number you quote from your manual look more like flooded Pb/A, not AGM, which would be typically higher than that--I'd expect to see 12.9-13.2 for fully charged.

Even by your numbers, 12.5 V is almost half discharged. Pb/A batteries of any construction do not like sitting in a discharged state, so the more you can keep your battery fully charged the longer it will last. I was just trying to get that message across.

I agree with you that the Prius is not good at keeping the 12 V battery fully charged, hence my encouragement to charge up when you see the (unloaded) sitting voltage to be at 12.5 V or less.

 

12.8 is almost a full charge.