Seemingly dead Prius turns on when touching negative battery terminal

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by clockworkjeremy, Dec 21, 2018.

  1. clockworkjeremy

    clockworkjeremy Junior Member

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    I have a very, very weird problem. Frequently over the past few months, my prius seems like it has a dead 12V battery. There are no lights on in the car anywhere, the car is nonresponsive to the remote or to the power button (with the smartkey FOB in our out of the slot). Shows all signs of having a dead 12v.

    The first time this happened, I grabbed my neighbor and had him pull his car over to give me a jump. I forgot the correct order that I am supposed to hook up the jumper cables, so I connected my negative terminal first. The second I touched the jumper cable clamp to the negative terminal of my battery, my car shot back to life. The other 3 clamps on the jumper cables were safely separated and definitely not touching eachother or anything but the dry concrete on the ground. I was very confused, but I thanked my neighbor even though he didnt do anything, I shrugged and went on with my day.

    This has now happened about 6 times since then. Each time, I have all the signs of a dead 12V battery, and yet the car comes back to life and turns on as soon as i touch a jumper cable clamp to the negative terminal of the battery. The car does in fact seem as if it was dead in the mean time. The radio presets are gone and the clock resets to 1:00.

    I put in a new yellow top Optima 12V battery myself (bought and using instructions from elearnaid) about 18 months ago and for the first 15 months or so, I noticed no problems, it worked great. I have tested the 12V per the instructions in many places on prius chat (here for example) and it tests just fine. ~12.3 Volts without load and ~10.7 Volts with load.

    Any guess what it is going wrong?? Is it possible I installed the 12V wrong? Why would touching the negative terminal and nothing else bring the car back to life, when im not completing any circuit?? Is the voltage test in maintenance mode not definitive and the battery itself was a dud and needs to be replaced?
     
  2. audiodave

    audiodave Active Member

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  3. padroo

    padroo Senior Member

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    Sounds like a bad battery ground connection. Make sure the terminals are clean and check the negative cable where it attaches to the body. Charge the battery and have it tested.
     
  4. audiodave

    audiodave Active Member

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    It's best to trickle charge those 12 volts on a regular basis. Prius charging system is weak.

    Posted via the PriusChat mobile app.
     
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  5. edthefox5

    edthefox5 Senior Member

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    Disconnect the ground lead from the chassis. Sand down the area it connects to and the end of the ground cable. Apply synthetic grease to that area and bolt that lead back up the car chassis please see my pictures. The red stuff is 100% pure ester base stock synthetic grease. No corrosion ever there.

    Then with ground lead still off on the battery side get some sandpaper and sand down the negative post of the battery till its nice and shiny then sand down the inside the neg lead ground post clamp. So everything is shiny and clean. Apply grease and bolt it back up.

    By the way voltage sagging to 10.7 volts means your battery is really bad and will leave you soon. You may notice when you hit the READY button and the car is booting up and all the dash lights come on for a second you will also see a bright red triangle flash for a second. That's the only warning you get the battery is bad. Next stop is car won't start.
     

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    #5 edthefox5, Dec 21, 2018
    Last edited: Dec 21, 2018
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  6. TMR-JWAP

    TMR-JWAP Senior Member

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    If you have a multi-meter. Set your meter to measure resistance. Hold your positive meter lead to the center of the (-) terminal post. Connect your negative meter lead to the car chassis (like the trunk latch, anything with bare metal). It should show 0 ohms. Now start touching and wiggling stuff to find out where the bad connection is located. If everything appears solid, it may be internal to the battery due to a bad mechanical connection between a bus bar and the terminal post. It happens.
     
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  7. clockworkjeremy

    clockworkjeremy Junior Member

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    Thanks for the replies everyone.

    I have tried wiggling the hell out of the negative terminal connection and it is on there very solidly. While wiggling and with the ignition off, but the headlights on, i wasnt able to get the headlights to go off or even flash, so i concluded that wasnt the problem. But that probably isnt a very good test.

    I will try removing the negative lead, sanding everything down to be nice and shiny and will grease up both the positive and negative terminals. If I still have problems, I will either get a multimeter (which i dont have), or take the car somewhere to have the battery tested.
     
  8. bisco

    bisco cookie crumbler

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    how old is the battery? maybe an internal fault
     
  9. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Did you check the negative cable where it bolts to the BODY?
     
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  10. padroo

    padroo Senior Member

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    It seems as though everyone is pointing in the same direction on this thread, I hope he replies.
    Some just disappear after their car is fixed never to return again. :)
     
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  11. clockworkjeremy

    clockworkjeremy Junior Member

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    I already did reply! I haven't had a chance to do anything about it yet though. Probably wont until tomorrow.
     
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  12. fuzzy1

    fuzzy1 Senior Member

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    The earlier symptoms clearly point to a bad / loose / broken connection somewhere, with a strong mechanical link to the jiggling or clamp compression of the negative terminal.

    Keep a very open mind about where the actual problem could be. Besides visible connections, it could be a broken connector or wire hidden beneath insulation, or even a broken post inside the battery case.

    Decades ago, when a dealership installed an AC kit to the first new car I ever bought, they disconnected a ground strap in the engine compartment. When putting it all back together, someone merely hand-threaded the bolt a couple turns then forgot to fully tighten it. I discovered some sort of problem a few weeks later when it failed to start late on a Saturday night in the next state. Jiggling things got it going, but I needed several more starting failures over the following week before finding the actual problem.
     
  13. padroo

    padroo Senior Member

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    Sorry, missed your post, good luck.
     
  14. ChapmanF

    ChapmanF Senior Member

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    It's possible for battery clamps and posts to feel totally mechanically tight and secure, and yet be oxidized enough even for stuff like this to happen.
     
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  15. clockworkjeremy

    clockworkjeremy Junior Member

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    So, it seems that the loose negative battery connection appears to have been the culprit. I took it to autozone and got a battery check and it came back in great shape. So, i bought some battery grease, greased up the negative terminal and the attachment to the frame, and tightened the heck out of both. Its hard to say for sure, but I havent had any problems since, so im declaring victory! Thanks everyone!
     
  16. terramir

    terramir Member

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    Hey letting you know I have a bosch battery and when I newly installed it on a trip I had simular problems thing is now that you tightened the heck out of it it might happen to you. The terminals are lead based and over time you might lose contact again. I had to buy some small hose clamps and make some "ring shims " out of em, i.e. undo the clamp and brake off the screw part and wrap it around the terminal to make the clamp smaller or the post fatter, however you want to see it.
    Just a hint for the future.
    My $ .02
    terramir
     
  17. padroo

    padroo Senior Member

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  18. ChapmanF

    ChapmanF Senior Member

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    Over-tightening lead battery clamps tends to squeeze their ends together and, eventually, make it impossible for them to achieve the necessary pressure on the battery post.

    Sometimes the overtightening is in an attempt to overcome bad contact because the battery post and clamp surfaces aren't clean enough. When they are clean enough to make good contact, the clamp doesn't need to be any tighter than the specified torque, and the connection won't give much trouble.

    Or, the overtightening can be because the clamp is already squished from prior overtightening, and now can't do the job. In that case, I'd say replacement clamps are pretty easy to get and less fuss than cannibalizing a hose clamp for a shim.
     
  19. terramir

    terramir Member

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    Yeah well I was leaving from watching the eclipse about 1k miles from my home and this was the fastest cheapest way to fix the problem at the time 3 bucks for a set of hose clamps, a few loaner tools and about 20 minutes of my time. And the repair has lasted 1yr 6mo. And 12 days and still going strong ;- )
    terramir
     
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  20. fuzzy1

    fuzzy1 Senior Member

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    I'd say that getting to experience that eclipse in person was very well worth this price.

    While that was my second totality experience, it was the first with weather good enough to actually see it. Wow!
     
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