CHG MODE Looks officially... GONE =-/

Are you sure it's not reaching max charge? Once the battery reaches "sufficient charged" which is 80% it cancels charge mode and goes in to HV mode. You can't use it if the battery is >= 80% anything above that you need to plug it in.

 

It was discussed on this thread a week or two ago:

Sold My 2024 Prime | PriusChat

The removal is only in North American cars - still there in Europe and Japan.

That makes me suspect it might be a regulatory thing, but I don't know what. If so, that might make it unlikely there's a way of resurrecting it.

One guess is that the change to 0W8 oil has prompted fuel economy rerating, and maybe there's been some new US or Canada rule about inefficient drive modes in the last couple of years.

I can't say I feel like it's much of a loss though - the only real use case is "driver error" - failing to have used HV mode when you should have.

In your scenarios of "people camping" or "wanting to have a charge to do city driving", you should have used HV mode to keep the wall charge until you needed it, rather than discharging so you end up having to use charge mode afterwards.

 

It might be possible to get it back, by simply installing the switch with the hold function. The Gen2 didn't have EV mode when introduced to North America. Just installing the switch, or hack circuit, restored EV mode. Why risk messing with software when removing the input device accomplishes the task?

As for why it's gone here, it could be for the same reason EV mode on the hybrid was excluded at first; to head of complaints of people who didn't read the manual and fully understand the mode.

 

You're the second person I've seen suggesting the magic is in the button. I'm a little baffled.

Seems like an amusing proposition - rather than a simple switch and a single wire, and connect it to one of your ECUs, put some sort of microcontroller into the switch itself so that it can time how long you press it, and then use some sort of protocol to indicate what type of press it was.

Do they do this for every button - they all have circuits that keep track of their "on" or "off" state, and send separate "on" and "off" indications to the computers?

Or, you could just have a single wire and a push button that closes the circuit whenever it's pushed.

That analogy doesn't work. That was a simple button that had been removed. There was no magic computer in it that made EV mode work - the ECU was always listening for a button press.

If the EV button had been a complex thing that sent a special "EV mode" signal, you wouldn't have been able to fit a simple button...

In this case, the simple button still exists - the input device hasn't been removed. But the ECU will have stopped looking for and taking action on long presses.

Your plan here depends on the EV/HV button working totally differently to the Gen 2 EV Mode button.

 

That was likely me. If the only difference between the buttons is the label, that brings up the question I proposed in that thread. Did anyone with a new NA PHV hold down the EV/EHV button to see what happens?

So sue me for not knowing there was no difference between the buttons.

 

I would dispute this "driver error' assertion for some cases, where an initial "wall charge" was not available, or not adequate, or the need exceeded the battery capacity. CHG mode would certainly be useful during some home power outages too.

 

If there was no wall charge available, that's still a form of driver error And you're still better off just running in HV. If it was more efficient to cycle through a wide range of battery in the absence of wall charge, that's what it would do. The Prius has never done that, for good reason, and efficiency is why an empty Prius PHEV sits with charge at "---", unless it can capture regeneration energy.

If you want continuous mains outlet power out of the car during the outage, I'd bet it's more efficient to just leave the car at "---" charge and let it cycle the engine on/off, rather than charging it up to let it drain back down from 80%.

Not least because a fair proportion of the output will be able to come straight from the MG, rather than going through a battery charge-discharge cycle.

If you want to suppress the engine overnight for noise, then charging up in the evening to let it use battery power for the night would be a use case, at the cost of some increased fuel use.

 

If an US i3 REx can have European operation restored, someone will find out how to return the charge mode. Just a question of demand.

 

That was a bit oblique for somewhat not familiar with the topic, but it was a useful hint.

It seems that the USA version of the BMW i3 REx had its range extender gimped so you couldn't select "hold state of charge" mode (ie equivalent to Prius HV mode), to meet CARB regulations so that it was classified as a "BEVx", rather than a "PHEV". And that ability was configurable so it could be re-enabled in USA cars via OBD.

Now, it seems that there are new CARB regulations for 2026 model years that refer to "charge-increasing driver-selectable modes", and require that some emissions tests are done in the worst case mode:

Almost certainly that, or some other paragraph in the same document, has got to be the reason for the removal.

Now, if the BMW i3 did manage to pass their CARB thing while keeping an OBD option to restore "normal" behaviour, it's certainly possible or even likely that Toyota may have done the same thing, and it's in there to be enabled, like the "Canada/Alaska/Greenland" heater behaviour is, even though not documented as a "dealer option". Toyota do like to put a hell of a lot of weird options in, and this feels like a case where they'd have wanted to keep it available if they could.

Main problem would be if CARB have tightened up and required that such things can't be re-enabled via OBD since the BMW i3 precedent in 2014. Haven't found any info either way on that yet.

 

The regulation in question was ZEV credits. CARB was assumed PHEVs were being driven in hybrid mode only for the program; regardless of hybrid mode being less powerful than EV or not. The hobbling was to let BMW get more credits per car sold. They could have sold the car as a PHEV for less credits.

The i3 is no more, so doesn't have to deal with 2026MY rules.
I am unaware of regulatory pressures on manufacturers for when to do a model year change over. Toyota could have avoided this feature delete by simply continuing to call the cars 2025s for longer. Or forgo the credits or whatever for not having the PHV not meet the low emission requirements, if demand for charge mode was high enough.

 

Yes, that's the point.

2014 rules may have let the i3 have an OBD option to violate CARB rules, but do the 2026 rules still allow it for the Prius? It's an example of a CARB OBD workaround apparently being permitted, but it's historical.

Sure, they could, for less than six months - they can't delay later than the start of the 2026 calendar year. (Rather smartly, rules that are based on model years do have a definition of model year that doesn't let manufacturers cheat by the cunning hack of claiming old years. )

But what would have been the point? Mess with their entire marketing calendar to delay making a minor inevitable change, removing a feature very few care about?

I suspect they were more worried about synchronising this change with the global 0W-8 oil switch.

There was some suspicion that there could have been a causal link there, but it seemed non-obvious, and it looks like they weren't related.

But it makes sense that you do multiple updates at the same time, to reduce number of different versions. It looks like a single July ECU update both removed (or made configurable?) Charge Mode and coped with the deletion of the low oil level sensor.

 

Bit off topic, but for what it's worth, that's exactly how the steering wheel buttons work in a gen 3 with the Touch Tracer display.

There isn't a microcontroller in each button. There's one in the steering wheel, and the buttons are wired to it, and it communicates about button touches and presses back to a module in the dash.

Without doing that, they'd have needed more wires in the spiral cable to carry the touch and press info for all the buttons.

 

Yeah, certainly at some point it's worth having something smart at the end-point to get the total wiring down. And the whole push for touch-screens generally is partly on that basis.

But Toyota's quite conservative on this, they're not doing it for 6 simple buttons on a console. And there are simpler solutions for a small number of simple buttons, like each button closing a single-wire circuit via a different resistance, and having an ADC at the ECU to deduce which button is pressed by voltage level. That's pretty common for normal steering wheel buttons.

That touch tracer thing presumably requires local smarts because it's not feasible to have capacitative touch detection done at the other end of a long wiring harness.

 

Removal of the “Charge Mode” is a shame. I have used it quite a bit driving my 2024 Prime. It’s handy to ensure that if the engine starts running it gets good and warm to get moisture out of the oil - especially in the winter.

On a road trip, it’s easy to forget to put the car back into HV mode after stopping for a meal or gas and at highway speeds the traction battery range gets used up very quickly. I was camping in the car and used the charge mode to get enough range back into the battery to keep the car warm overnight without having the engine start up.

Also, I have found the Charge Mode seems to be surprisingly efficient and not that different than driving in HV mode in terms of mpg.

 

It's not capacitive, AFAIK, just a lighter (but definite) level of pressure.

In the trim levels without Touch Tracer, there is no microcontroller in the steering wheel, and the buttons-and-different-resistances trick is used.

The microcontroller allows them to built the Touch-Tracer and non-Touch-Tracer trims without needing a fatter spiral cable for TT.

 

In the US, aftermarket software 'tunes' aren't certified by a regulatory body. Many even have a stealth mode to hide it, and revert to factory, when going into a dealer. A California registered I3 REx with the EU settings would likely be fined for emissions defeat device if caught.