Red triangle during the idle calibration "dance". Straight after 12V replacement,

Hi all, I've been absent from the forums for a few years. Good to see a lot of the old familiar posters still here.

My current problem :

- I just replaced my 12V battery after the old one died suddenly yesterday.

- No problems there. I did it myself and the new one is showing good voltage levels (both when running and when off).

- First drive after changing the battery I tuned the radio and set the clock and everything seemed totally smooth.

- Right up until it was fully warmed up and I stopped at a set of lights with the engine idling. It started doing it's usual Gen2 calibration dance, where it normally idles for about 8 seconds before cutting the engine out. But after a few seconds the Red triangle exclamation mark and "problem" lights came on.

- I pulled off the road and turned it off and on again, but the warning lights remained. I also checked the oil and fluids and serpentine belt, and everything looked perfect.

- I then had to drive it about 12 km home with all the warning lights on, but surprisingly the car seemed to behave perfectly. Engine power was normal, battery charging and EV running was normal, MPG was excellent. I really couldn't detect any problems, but the big triangle and !problem! warnings remained.

- When I got back home I pulled the little plug with the single white wire at the 12V battery terminal block (and old trick I learnt here to reset the codes without disconnecting the battery). This reset the codes, and surprisingly they have not returned (driven about 100 km since).

- BUT, there is one remaining problem, and once again it is related to the little calibration dance that the Gen2 does after it warms up. Instead of cutting out the engine after about 8 seconds as it used to do, it now takes about 40 seconds every time!

Just wondering if anyone else has experienced anything like this after 12 battery replacement? I'm wondering if it's just some dodgy data in the system somewhere after the 12V failure (it was down around 7 volts and my wife was trying to start it with relays dropping in and out and sounding very unhealthy), and if maybe it will just sort itself out after driving it for a few weeks?

Unfortunately I don't have a scan gauge or similar to check for codes, but all warning lights are staying off and the car appears to be otherwise running perfectly.

 

No I don't think so. The HV battery was replaced (with a new one from a dealership) a few years ago and it has been performing flawlessly.

It runs without any problems in EV mode, and the SOC seems to be behaving totally normally (charging and discharging as expected with no rapid fluctuations or anything). It really seems to be running perfectly apart from that one strange issue.

 

Yeah I should have mentioned that JC. I pulled over and checked that as soon as it first popped the warning lights. Oil, coolants (both), inverter pump flow, serpentine belt and 12V battery voltage. All were perfect.

The warning lights seem to be staying off for now. It's just that I suspect something is still not quite right as it still doesn't do the idle check and cut off the engine properly.

 

Just an update.

After a couple of days driving (about 220 km) it seems to have come good all by itself. It looks like my Prius is just a slow learner, but at 15 y.o and 383000 km I think I can forgive it for that.

Last night I had a few errands to run, and it let it cool a little between each trip to make sure that it had to redo the idle thing. Each time it got better and in the end it was cutting out the engine in about 5 to 8 seconds of idling, which is totally normal in my experience.

Now my lead footed wife has taken it to work today, so it's sure to get a good "Italian tune up" as well.