Help! Prius doesn't shut off ICE

Even with the engine warm, the ICE can run. If you have the heat on, it will keep the ICE running more to keep you warm. If the battery is discharged too much, it will keep the ICE on to charge it up again. If the AC is on, it will keep the ICE on more, because the battery discharges faster.

 

Doesn't it also run to keep the catalytic converter hot?

 

Hi antuanous. Read up about stages 3b and 4 of the prius operation here : http://www.techno-fandom.org/~hobbit/cars/five-stages.txt. This may provide your answer.

In particular check the following. Once warmed up check if you can indeed glide so long as the speed immediately prior to the glide is 55km/hr or greater. If this is the case but it wont glide when you start from under 55 km/hr then it's caused by the dreaded "stage 3a" operation. In this case try stopping the car with the engine idling for 5 to 10 seconds until the motor shuts off (has to be fully up to temperature ok). Now when you continue it should be in "stage 4" and the engine should turn off every time you glide.

I know it's weird and I know it's annoying, but seriously that's how it works in the Gen 2.

 

What uart said.

It's quite annoying to accelerate up to an indicated 38mph just so the engine will switch off, if you're in traffic. 29mph - the UK EV speed limit, indicated (actual about 26-27 for me) - is too slow for a posted 30mph limit.

In the past others have reported 'engine doesn't switch off immediately when coming to a stop in "B" mode'. I can't say I've ever experienced this. I know that sometimes after a very long descent, that has fully charged the battery, the car will spin the engine to throw away some charge. However, I suspect it's actually just the warmup again - using "B" mode, which spins the engine as an air pump, causes the engine to heat up. Indeed I use "B" mode deliberately in winter to warm the engine quickly.

Thankfully on Gen 3 it appears the requirement to drop below 8mph and use no power for 10 seconds (you don't have to come to a complete stop, just slow enough that the engine computer registers 'idle') has gone.

I note that the service manual indicates that there is a software monitor, for DTC P0101 (Mass Air Flow Meter Rationality), that runs for 10 seconds and requires that the engine is idle and that the coolant temperature is over 70°C - exactly the conditions mentioned. I suspect it has to run this monitor before it thinks it can trust the signals coming from the MAF and therefore enter closed-loop fuel control (where it computes the amount of fuel to inject based on the mass of air entering the engine and the oxygen level in the exhaust gases, using the Air-Fuel Ratio Sensor/O2 sensor).

Some owners have reported significantly better fuel economy after the idle check has completed than before, even when running well over stealth mode's speed limit of 42mph.

 

That's an interesting bit of extra info there mike, thanks for that.

 

+1. I don't remember seeing this kind of detailed info in other discussions about Prius warm up stages.

 

Now I understand partly what's going on with mine.

I had all coolant fluids changed (inverter, engine) along with new spark plugs and transaxle fluid, so far, the cars ICE has stopped running all the time...it always shuts off when it is supposed to like it did when I first bought it (used)

Not sure what was causing it for sure, but I hope it doesn't return.