PS + Main + exclamation after 12v battery swap!

[wwu123]

What a scare! I decided to change my 12v aux battery in my 2002 classic as a preventative measure, as it was the original battery going on almost 8 years. It was still showing 12.3 volts and our California winters are fairly mild. There were no apparent issues, though after 120K miles my mileage seemed to be dropping a few MPG from a few years ago. So I ordered one of those highly recommended Exide spiral batteries, and picked up the replacement kit from TSB EL014-03 that would have the larger tray and terminals that would fit, according to forum posters here. I trickle charged it for a few days to make sure it was fully charged.

After swapping everything out and verifying 12.75 volts with the new battery, and radio and other aux functions showing normal operation, I started it up and immediately got a red triangle of death, followed by the dreaded PS + Main battery + exclamation point. Then the rough idle stalled out after about 15 seconds. Turned it off and tried again, same problem. Rechecked terminal connections and ground wire to make sure they were secure. Same problem.

I was worried that the new battery was defective and showing low voltage under load, so I swapped back in the original battery to make sure it was the battery and not the car. Still had the triangle of death and stalling. Now I was really worried I'd blown a fuse or shorted something out in the car. Checked the small and large fuses in the red terminal connector, they seemed fine. Checked that I didn't pull loose any wires in the terminal connector, seemed like there was only a single brown one that was still secure.

Come online to Priuschat and find other classic owners have seen this when disconnecting the aux battery, but most threads end unresolved or with some recommendations about a sticky throttle body, main battery issues, or to go to the dealer. Still convinced it's related to the disconnected battery, as my car has been running fine for years. Finally come across a few threads like this one starts then dies.

I try what worked there, putting it into neutral right away and leaving it there for a few minutes. Sure enough, the ECU or whatever fixes itself and the errors go away. I drive around for a few minutes and everything is fine again.

Apparently this seems to be common situation if you disconnect the aux battery for too long, that the ECU gets confused during initialization or something. How terrible though that the car will actually idle rough and then stall out, even though there is nothing wrong with the aux battery or apparently anything else. Without otherwise knowing how to deal with this, the only recourse would be an expensive tow and trip to the dealer, and possibly some unnecessary repairs. Posting this just so there are more threads on trying this solution before folks end up with a multi-hundred dollar trip to the dealer...

[tochatihu]

Thanks, we are always interested in what works. We can figure out why later! I'd guess that your car has an unusual 'fuel map' (relationship between throttle butterfly angle and fuel injector milliseconds), for whatever reason. Disconnecting the 12 would cause that relatinoship to be forgotten, so the ECU would use default values. Without much success. Any way to get the relearning started would be the right way.

It might be wise for all to think about backup 12 volt power during battery changes, etc. if there are more important things than radio stations being forgotten

PS: what's with the 12 guests viewing this thread - spambots?

[Patrick Wong]

Originally Posted by wwu123

...I try what worked there, putting it into neutral right away and leaving it there for a few minutes. Sure enough, the ECU or whatever fixes itself and the errors go away. I drive around for a few minutes and everything is fine again.

Apparently this seems to be common situation if you disconnect the aux battery for too long, that the ECU gets confused during initialization or something. How terrible though that the car will actually idle rough and then stall out...

Thanks for reminding us about this Classic Prius issue. When I replaced the 12V battery on my 2001 a couple of years ago there were no problems - however it did have the latest revision engine ECU installed.

It's good to keep in mind that a problem like yours might come up (which probably is related to the engine ECU), and if so, know what to do about it. I'm wondering whether the engine ECU was ever replaced on your car?

[wwu123]

Not that I'm aware; there was a first owner until 2004 who did have all their maintenance work and some TSB's like the "battery sealing" done at the dealer. Was there ever a TSB on the ECU that they may have done?

[Patrick Wong]

Pls note that there is a difference between an TSB and an SSC.

TSB or Technical Service Bulletin advises the Toyota tech about a known problem, and what to do about it. Warranty coverage info is on the first page of the TSB. If your car has the problem but is not covered under warranty, then you have to pay for the repair.

SSC or Special Service Campaign is aka a recall. The traction battery sealing is an example of an SSC, and this would be done at no charge regardless of warranty status.

Back to your original question: a TSB was issued on the engine ECU for no-start situations. The engine ECU is located behind the glovebox. If you can get back there, check the part number label: 47054 is the part number suffix for the latest version ECU.

If your ECU is downlevel and you want to do something about it, you could try buying a salvage ECU for around $300 or so. A new part would cost around $1K.

[wwu123]

Thanks for the tip. I was just behind the glovebox a few weeks ago changing out the cabin air filter, so I went back to check it and the ECU is 89661-47051, probably the original one. The car has been running fine on two errands today, so I won't change out the ECU just now. I see you've helped out a lot of other folks on addressing ECU-related no-starts, so good to know in case I get a no-start in the future.

I've found more threads where folks encounter this, no necessarily after a battery disconnect, and the stalling is generally alleviated by shifting to neutral or revving the RPM's in drive quickly. Anyone know why the ECU is suspect to this condition, and possibly might be only the older ones? It did seem that even after I got it into drive yesterday, it was still running and idling a bit rough for about 10 minutes (and wouldn't go into stealth even at stops). Then it finally "learned" enough and calmed down. Today it's running really smoothly again, and I may even have gained a few MPG's, though trips have been too short to really tell.

[wwu123]

So just by chance this week, I had to give my co-worker a lift after a meeting as he sprained his ankle and couldn't drive. He sees my car and says "oh, you have a Prius too", as it turns out he has a 2001. He then goes on to say he's never had a problem in nearly 9 years until a week ago, when the car started with funny sounds and quit, plus a bunch of warnings on the MFD.

He ended up towing it to the dealer, where they traced that a 12v battery cable was loose, and charged him $300 to fix the problem (not sure if they actually replaced any parts). After I described what happened to me he's sure the exact same thing happened when his cable disconnected power for too long, and that he could've avoided the whole $300 + towing cost if he'd found the trick that I did.