Can a Gen 4 prius run out of its hybrid battery in ignition on mode

Your Prius will not let the HV battery get "empty". It will usually start charging at 40% with no request for motive power (earlier if you as it to accelerate) and with no bars is still at 20%. There will always be some reserve power to start the ICE unless there is a problem with your Prius.

JeffD

 

Nope. Charging circuit kicks in at 20%

 

do not use ig on mode, put it in ready to avoid catastrophe

 

In ignition ON mode (unless Gen 4 really drastically changed something), the hybrid battery isn't even in the game.

Nothing that happens in ON mode happens to the hybrid battery.

You can definitely discharge the 12 volt aux battery that way, though.

If the hybrid-battery bar graph changes at all while the car is in ON mode, that's just the battery ECU revising its opinion of how charged the battery is. It isn't the battery really gaining or losing charge, because in ON mode it doesn't.

Again, unless there is something about Gen 4 that is absolutely different in this respect from all other Prii.

 

Welcome, @Alkanator.

Apparently the 1st three responders missed that you had it in ignition on mode. As usual, @ChapmanF nailed the answer. As with previous generations, leaving the car in ON or ACC will kill the 12v battery. The traction battery is isolated by a relay unless you put the car in READY. Leaving the car in ACC or ON for more than a very few minutes is a really really bad idea. If you leave it in READY, the traction battery will keep the 12V charged and, if the traction battery gets below a certain point, the ICE comes on and charges the traction battery.

 

Any occasional change you might see to the traction battery SOC when not in READY mode is just the system updating its information from the sensor wires.

I'm absolutely 100% sure that neither ON nor ACC use the traction battery. I highly doubt that you'll find anyone here who would agree with you. That's why the car shuts itself off to protect the 12V battery after 20 minutes to an hour in ON or ACC depending on which mode you're in. The relay only connects the traction battery to the car in READY mode. If you pay attention, you'll probably hear that relay when you put it in READY, but not in ON or ACC. Anything that runs in ON or ACC is coming from the 12V battery.

 

'decreases once in awhile' doesn't give us much information. doesn't gen 4 shut off after 20 minutes in ig on mode?

 

You have observed that correctly, and the reason is that the air con compressor runs on high voltage from the hybrid battery, which is never connected except in READY mode.

 

you have the 'special edition' battery

 

Only the HVAC fan was on. As @ChapmanF said, the compressor runs on high voltage from the traction battery, which is only connected in READY mode. If you look at the manual, it says that the car will shut off after 60 minutes in ACC mode (which lets the fan motor run) and further states that that "cannot entirely prevent" the 12V battery from discharging. It doesn't say that it will discharge the battery every time. Who know what loads you're running or how charged up the 12V is when you do that.

If you want to sit in the car with AC, radio, etc, do it in READY mode. Your wallet will thank you. And do not neglect the owners manual for this car. It's not just a kneeling pad like most car owners manuals. Read up on it and you'll be seriously happy with your car.

 

1. With POWER ON - it's ready to drive, the A/C works, the Hybrid battery is in action, the 12v is being force-fed as required by the Hybrid Battery, and if parked for an extended time, PETROL is used by the ICE to keep the Hybrid battery topped up.
2. With ACC - nothing much happens - but some electrical gadgetry still works - it can FLATTEN the 12v, but the Hybrid Battery couldn't care less!!

If you have DRLs, you'll want them off when parked with POWER ON and A/C running:

You need to stop, shut down, and restart WITHOUT changing from "P", the DRLs won't come on till you select a gear.. If you decide to reverse/fwd 6" to get a better alignment, the DRLs come on again - start the process again.

This was an article about it in relation to going to the Drive-In:

Going to the drive-in | PriusChat

 

It looks like you have condensed the four power states into only three. There are four.

• OFF - nothing much has power, except ECU memories, smart key transceivers, dome lights, horn, head/taillights if you turn them on, etc. Stuff like the brake system or evap system self tests can run while OFF, or the brake pump start when the driver's door opens.
  
• ACC (foot off brake, one button push) - most stuff still off, except for the infotainment system.
  
• ON (foot off brake, two button pushes) - most 12 volt stuff in the car is powered. The dash display and most warning lights are on. HVAC controls will work and the blower will run. Not ready to drive, the A/C does not work (except for the blower), the hybrid battery is not in action, and the 12 volt battery is not being charged. In fact, ON discharges it faster than ACC does, because more of the car is powered.
  
• READY (foot on brake, button push) - The word READY is shown on the dash. It's ready to drive, the A/C works, the Hybrid battery is in action, the 12v is being force-fed as required by the Hybrid Battery, and if parked for an extended time, PETROL is used by the ICE to keep the Hybrid battery topped up.

In sum, as mentioned earlier in the thread, the hybrid battery is not connected in any state except READY.

 

Yep - I forgot about the "2 PUSH" mode - I've never used it, couldn't see any point in it - I only ever use 1) OFF (obviously) and 2) "READY". There has never been a time here where I wanted it ON without A/C - but I suppose it could happen.

 

ON is used in a lot of diagnostic procedures; all the ECUs have power then and will communicate with Techstream.

It's also handy if you realize you've forgotten to roll up the windows.

 

Ahh - if that happens, here in Australia we just long press the LOCK button to roll up all the windows - something I think was missing in USA.

 

Just to throw a monkey wrench into this discussion of ON mode, I just found out on all new Japanese (note this may be only on Japanese models) Toyota Aqua (aka Prius C), which is now equipped with an AC100V/1500W inverter system, there is a special ON mode operation to let one use the AC100v outlet in the car continuously with occasional engine kicking on as needed. Yes, the Toyota Japan site says a tank full of gas would provide 5 days worth of electricity to the average Japanese home on this special ON mode.

AFAIK, none of the US models of Prius or any other Toyota hybrids has this functionality, but if it comes to the US... there will be an all-new use of ON mode.

The following linked page explains the procedure on all new Japanese Aqua, but it is in Japanse.
トヨタ アクア | 特長 | トヨタ自動車WEBサイト

 

There was another recent thread about that new Aqua, where the announcement mentioned a new "emergency power supply mode", which I took to be a way you could get the car "READY-like" for use of the inverter, without it automatically shutting down or letting passers-by drive it away.

I did not see any owner's manual excerpts to see exactly how one gets into the "emergency power supply mode". I would probably talk about it as a distinct mode from ON ... technically it is more "READY with limitations" than "ON with extras".

Already in some Gen 3s was a "remote A/C" mode that is a kind of "READY with limitations", in which the air conditioning works.