2001 Prius - dead battery with continuous horn

[NYCpriusdriver]

Hi everyone,

I hope this is the right forum for this. I've searched everywhere and haven't found the specifics of my problem so I feel there might still be hope. I live in New York City and rarely drive my 2001 Prius at all since I moved here 4 years ago. Before that I used to drive it a lot more, but it still only has 50,000 some miles on it.

I've been trying to take it on a good drive at least once a month. Sometimes I need to hook up a charger to the 12v or use a booster battery to get it going. This has worked up until now.

A couple weeks ago I started it with the booster and let it run until the engine shut off. I know this doesn't completely charge everything but I turned it off and it started again without the booster. So then a week ago I tried to start it again with the booster and got nothing except the hazard lights went on solid.

Since then I've been charging it with a Vector 2/6/10 amp charger on the 2 amp setting. After over 12 hours of charging it said it was charged, but if I disconnect the charger and connect it again after a while it still takes more of a charge.

Before I got the 12v supposedly "charged" and again after, at a certain point the horn would come on and stay on continuously. I either had to wait for it to drain the battery enough to shut off or disconnect the battery which I finally did. Now I'm charging the 12v by itself, when I connect it I still get nothing, no lights, nada, but if I hook up the charger while it's connected then the horn will still come on.

It would at least start two weeks ago. I highly doubt the traction battery has completely died in that time. The 12v battery was replaced less than three years ago so I could just need a new one but I'm hoping I can get at least one more start out of it so I don't have to get it towed. Any thoughts? Any advice much appreciated. (Also if anyone is really interested in acquiring a first gen Prius considering the above, please send me a PM).

[JimboPalmer]

Your car is a First Generation Prius ('2001', 'first gen') but you have posted this in a Second Generation Forum (Gen II Prius Care, Maintenance and Troubleshooting) This will reduce the number and accuracy of the answers.

[NYCpriusdriver]

Originally Posted by JimboPalmer

Your car is a First Generation Prius ('2001', 'first gen') but you have posted this in a Second Generation Forum (Gen II Prius Care, Maintenance and Troubleshooting) This will reduce the number and accuracy of the answers.

Thanks, but I didn't see any first gen forums on this site. I started to post in the newbie forum (even less technical I figured) and it came up with similar threads involving 2001 Priuses, all in the Gen II forums. If a mod could move my thread to the appropriate forum that would be great.

[Patrick Wong]

Originally Posted by NYCpriusdriver

...A couple weeks ago I started it with the booster and let it run until the engine shut off. I know this doesn't completely charge everything but I turned it off and it started again without the booster. So then a week ago I tried to start it again with the booster and got nothing except the hazard lights went on solid.

Since then I've been charging it with a Vector 2/6/10 amp charger on the 2 amp setting. After over 12 hours of charging it said it was charged, but if I disconnect the charger and connect it again after a while it still takes more of a charge.

Before I got the 12v supposedly "charged" and again after, at a certain point the horn would come on and stay on continuously. I either had to wait for it to drain the battery enough to shut off or disconnect the battery which I finally did. Now I'm charging the 12v by itself, when I connect it I still get nothing, no lights, nada, but if I hook up the charger while it's connected then the horn will still come on.

It sounds like your 12V battery is dead, but I am also wondering why the horn is sounding when the charger is connected. Do you have an aftermarket alarm system installed?

To verify that the battery is bad, assuming that you don't have access to a voltmeter, you could try turning on the headlights to see whether the lights are at normal brilliance (with the charger disconnected). If the lights are dim, that is strong evidence the battery is dead or close to it.

It's generally not a good idea to use the "booster" function of the battery charger to start the Prius. The reason for this is that the voltage produced by the charger under that condition is relatively high, and may damage the Prius ECUs. If you follow the Toyota TSB advice on battery care, you are supposed to disconnect and remove the 12V battery from the car before charging it, to eliminate any possibility of damage to the vehicle.

To avoid having to tow the car, is it reasonable for you to take a cab to a local Toyota dealer so that you could buy the correct 12V battery and install it yourself?

[NYCpriusdriver]

Originally Posted by Patrick Wong

It sounds like your 12V battery is dead, but I am also wondering why the horn is sounding when the charger is connected. Do you have an aftermarket alarm system installed?

No, it's the same one it came with. Before when I've brought it back to life the alarm system would come on with the horn intermittent, but something different seems to be going on here.

To verify that the battery is bad, assuming that you don't have access to a voltmeter, you could try turning on the headlights to see whether the lights are at normal brilliance (with the charger disconnected). If the lights are dim, that is strong evidence the battery is dead or close to it.

For the last couple weeks I haven't been able to get any lights to come on at all. No trunk light, no dome light, nothing. Just the horn. I managed to dig up a voltmeter and it read 14~ with the charger (the charger also has this function) and 12~ when I took the charger off. I also got a quick 10A reading along with a spark but I didn't want to risk blowing my meter. Seems like it's still got some juice in it and the capacity to hold some.

It's generally not a good idea to use the "booster" function of the battery charger to start the Prius. The reason for this is that the voltage produced by the charger under that condition is relatively high, and may damage the Prius ECUs. If you follow the Toyota TSB advice on battery care, you are supposed to disconnect and remove the 12V battery from the car before charging it, to eliminate any possibility of damage to the vehicle.

The booster and the charger are two devices I bought separately. I've never had them hooked up at the same time. I'll keep that in mind for the future about disconnecting the battery before charging it but it hasn't been a problem up until now. I assume the booster is just a smaller battery which you charge separately and the Prius just draws whatever it needs from it when you hook it up.

To avoid having to tow the car, is it reasonable for you to take a cab to a local Toyota dealer so that you could buy the correct 12V battery and install it yourself?

I could probably even take the subway, but with the battery appearing to at least hold a charge for a little while it makes me wonder if something else isn't going on. There may well be a problem with the ECU or another computer component that only a dealer would know anything about. Maybe there's just a fuse that needs replacing? Thanks for the help so far.

[Patrick Wong]

Originally Posted by NYCpriusdriver

...For the last couple weeks I haven't been able to get any lights to come on at all. No trunk light, no dome light, nothing. Just the horn. I managed to dig up a voltmeter and it read 14~ with the charger (the charger also has this function) and 12~ when I took the charger off. I also got a quick 10A reading along with a spark but I didn't want to risk blowing my meter. Seems like it's still got some juice in it and the capacity to hold some.
...Maybe there's just a fuse that needs replacing?

Yes, this would also explain why the car is not starting. It sounds like you will need to check the fuses by removing them one by one and measuring each fuse's resistance with an ohmmeter. The resistance of each fuse should be very close to zero.

If you can find the DOME fuse (which powers various instrument panel circuits, i.e., much more than just the dome light) you'll may find that it has blown. If that fuse is OK, then another fuse upstream from that (or maybe a fusible link) is probably the problem.

As I'm traveling currently, I don't have access to the wiring manual. If you have trouble finding the fuse(s) that need replacing, you might want to consult your owner's manual. If you can read the wiring diagrams, you may want to download them at techinfo.toyota.com

If the "booster" is just a compact-sized 12V battery, then no worries about its use on Prius.

Good luck.

[NYCpriusdriver]

Originally Posted by Patrick Wong

Yes, this would also explain why the car is not starting. It sounds like you will need to check the fuses by removing them one by one and measuring each fuse's resistance with an ohmmeter. The resistance of each fuse should be very close to zero.

If you can find the DOME fuse (which powers various instrument panel circuits, i.e., much more than just the dome light) you'll may find that it has blown. If that fuse is OK, then another fuse upstream from that (or maybe a fusible link) is probably the problem.

As I'm traveling currently, I don't have access to the wiring manual. If you have trouble finding the fuse(s) that need replacing, you might want to consult your owner's manual. If you can read the wiring diagrams, you may want to download them at techinfo.toyota.com

If the "booster" is just a compact-sized 12V battery, then no worries about its use on Prius.

Good luck.

Thanks. I think this got me over the hump. I didn't really know where to start with the fuses and most of the big ones are opaque. Upon examination, three 15amp fuses are visibly blown. DOME and also AM2 and THRO. A visit to the auto parts store tomorrow during lunch should take care of this. The battery is now charging at a steady 2.2-2.3 amps so maybe it got past its false charged state and will be full by tomorrow.

Thanks again. I'll post a follow-up to help out the few others out there still driving around in first generation Priuses.

[Patrick Wong]

Originally Posted by NYCpriusdriver

... Upon examination, three 15amp fuses are visibly blown. DOME and also AM2 and THRO. A visit to the auto parts store tomorrow during lunch should take care of this...

Pls note that the fuse physical size is non-standard, so your local discount auto parts store may not have the right replacements. I suggest you bring a blown fuse when shopping. You may need to visit your Toyota dealer to obtain the correct fuses.

I hope that the replacement of those three fuses helps, but I am concerned that a fusible link may also have blown. Then there's the question of why the fuses popped in the first place?

[tochatihu]

Hate to mention the possibility that blown fuses could have resulted from an accidental polarity reversal when connecting the external power source.

[NYCpriusdriver]

No, no polarity reversals but they may have blown either from the booster battery or from briefly having the charger on the 6 and 10 amp settings. Stupid, I know, but I just wanted to get it going and wasn't going to do it very long. I learned my lesson. Also I had gotten in the habit of boosting it with the key set to "on" so the alarm wouldn't go off. No more of that either.

So here's the latest:

The fuses did the trick and now it starts. But only for a few minutes, then it kind of sputters and shuts off. Trying to start it again kicks on the horn, windshield wipers and maybe an engine alert or two. I left the battery charger on overnight and it switched to automatic float charge, but I didn't want to leave it on during the day while I was gone so I disconnected it. Tried it after I got home and put in the fuses, it started but didn't last so I charged it some more and hooked up the booster.

It seems to do okay with the booster connected but I don't think the battery can hold a good charge or maybe it isn't charged sufficiently to where the alternator (or whatever it is on the Prius) can keep it charged. I'm guessing it may have been deep cycle discharged, which I've read conflicting things about whether or not that means it's toast. It was replaced I believe in late fall 2006 so it's still less than three years old. Right now the battery is back to drawing 2.5 amps or so from the charger and I can try that for a few more days. After a little more playing around I'll probably try and drive it to the dealer, maybe with the booster connected the whole way but taking local roads in case it completely dies on me en route. Surely even on the '01 Prius they thought of some way to automatically test the integrity of the 12v battery so it doesn't die in the middle of the road???