2001 Prius - dead battery with continuous horn

[tochatihu]

Good news on the startup - it excludes some scary options. We have to get you on a known-good battery. Are you aware of the throttle butterfly and induction cleaning procedures? Do you have sufficient fuel in the tank?

Sorry, I know of no other long distance approach than taking tiny steps.

[Patrick Wong]

Glad to hear you are making progress.

If your booster is just another 12V battery, then I think you should try disconnecting the Prius 12V battery, and rely solely on the booster battery. See if that helps or not.

[NYCpriusdriver]

Throttle butterfly and induction cleaning procedures? Don't know anything about those but if you can point me to a good source I'm willing to give them a try. The tank is almost completely full, still has all ten bars on it.

The booster battery is a Black & Decker somethingorother, I don't have the specs in front of me. It's smaller than even the Prius battery. I think it says it can deliver a maximum of 200 amps. I'll have to look and see if it says anything about driving on it as the sole 12v battery (of course they probably don't address driving on it in combination with the HV battery). If I did drive it solely with the booster battery, I wouldn't want to do it for very long.

One thing I haven't had time to do yet is start it after the 12v battery has just been completely topped off by the charger. If it drains while it's not charging during the day then I'm guessing it either still has a long way to go to be fully charged or it has serious problems and needs to be replaced. Hopefully I will have time by this weekend to try this but a rain forecast in the next few days is going to complicate things, although I might be able to cover it with a tarp. In the meantime I'm just going to keep charging it whenever I can, assuming the charger is smart enough not to damage it by overcharging at 2 amps.

[tochatihu]

See Bob's how to:

Cleaning Prius Throttle

If your Prius battery cannot hold a charge it needs to get gone. Lead recycler, or doorstop.

[NYCpriusdriver]

So I'm going to give this maybe one more try before I break down and take it to a dealer. Again, sorry this is in the wrong forum. I swear I didn't see the Generation 1 forum before (maybe the link was different?)

I went ahead and ordered then installed the Miata battery from eLearnAid and it seems fine. It was testing at 12.6v out of the box so I didn't charge it any more initially. I installed it Wednesday, it started fine and seemed to stay running so I shut it off. Saturday I took it out on an errand for about an hour. No problems during the trip except what I had been neglecting to realize was a bigger problem this whole time: since I replaced the fuses, the interior lights work and everything comes on when I turn the key to ON, but in ACC mode none of the accessories or anything come on. I did notice a whirring sound of some sort when I hold it in ACC mode, then when I turn to on the engine starts along with a brief beep from the horn and the windshield wipers wipe once. This behavior has been consistent with both the old and new battery since I replaced the fuses.

To top it off, when I got back from the errand I left it running for a while and the engine stayed on longer than I thought it should while I was trying to call Car Talk (didn't realize they call you back first and don't take live calls). It seemed to sputter and die during this time and when I tested the voltage it was only about 11.5. I broke out the charger and charged it overnight and got it up to 13.5, and then I got a ! triangle after starting it but still nothing when the key is on ACC. The battery charger does have an alternator check which I tried and it came back bad, but it does say your specific model of car may have crazy electronics which are not compatible with the alternator check.

So it appears the 12v battery is not being charged, and I can only assume this is related to ACC not coming on. I've tested the ACC fuse along with most of the others and they all have low resistance, and all of the non-opaque ones visually look good.

note: I know this is already long-winded, but for anyone who cares about the surrounding details: if possible I need to take this car on a 1,000+ mile trip in late November to be inspected in another state. I'm hoping against hope that since I'll have to take it to a dealer then anyway, I can just wait until then to have any major issues looked at in one shot. Bad idea?

[Patrick Wong]

If the radio and other accessories don't work when the key is at the ACC-ON position, then you must have more fuses that are bad, or a bad relay.

Prius does not have an alternator so please do not use any tests that are not intended for that car.

Do you have a digital voltmeter? If so, measure the voltage across the battery when the Prius is READY. What voltage do you get?

If ~13.8V then the 12V battery is being charged. If much below that, then the battery is not being charged and the DC to DC converter within the inverter is probably bad (or the DC/DC 100A fusible link has blown).

There's no way you will be able to drive 1,000 miles in that case, you'll have to seek help from a local Toyota dealer.

[tochatihu]

I hope it's the fusible link! perhaps we don't have a good how-to on testing or replacing that. First use your owner's manual to identify the correct under hood fuse box. Disconnect the 12 volt. Unbolt the fuse box and test the connections underneath for continuity.

[EZW1]

Note: My owners manual says to adequately charge the 12V by letting the car idle, you've got to leave it on for 1/2hour. Most people do the 5 to 15 minute thing and that may not be enough.

[NYCpriusdriver]

Thanks everyone for your help, but I made an appointment to take it to the dealer tomorrow morning. Since I know I can at least drive it that far I think I'm just going to do it. I tested the voltage with the engine running and it drops down to about 11.5v so I don't think there's any way it's charging. I tried to take the 110A DC/DC fuse out to test it and ended up popping the clear plastic cover off. At least I saved a few bucks and hopefully got a better battery with the Miata battery. If they try and charge me an arm and a leg for something that's simple and possible to do myself, maybe I'll give it another go. I'll let you know how it goes.

[Patrick Wong]

Originally Posted by NYCpriusdriver

... I tested the voltage with the engine running and it drops down to about 11.5v so I don't think there's any way it's charging...

My guess is that the inverter has failed. If so, then the dealer will probably charge you around $3K to replace it.

An alternate approach would be for you to buy a salvage part for $1K and install it yourself.