Random electrical issue

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by schmuber, Oct 10, 2018.

  1. schmuber

    schmuber Member

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    Had a rather hairy experience with my beloved 2010 Prius… as I was driving in the middle of nowhere, the horn went on (constant on, not pulsating). It killed my 12v battery in less than a minute, with random error indicators and "P lock malfunction" to boot. Oh well, probably just a weak aux battery, right? I waited for the auto parts stores to open and bought a brand new one. Installing it cleared the error messages, but not the stuck horn.

    Unplugged the horn, went online to so some research. Learned about the integration relay (thanks Toyota!), found the test points on it… Both should read 3.5 to 5v, but on my car only D1 read 4.8v. D2 read 0. According to workshop manual found online, "If the result is not as specified, one of the electrical load (sic) connected to the integration relay may be malfunctioning."

    "May be"?! I'm a full time Uber driver, I need a car to earn. And it caught me in the worst possible moment, while I was dealing with another emergency. I couldn't afford a visit to a proper mechanic, and somehow I doubt that any garage will have payment plans for a service. Oh boy, I'm dead in the water.

    So far the symptoms suggested the clockspring cable or an integration relay malfunction. Car seems to be running quite normal… or so I thought. Tonight I've decided to take a risk of hitting the road on a car with disconnected horn. Luckily, less than a mile from home I've noticed another troubling symptom that made me come back immediately: high beams were slightly flickering out of sync. That's just plain wrong.

    Any ideas or suggestions?

    PS. A few more details that seemed random at first, but now appear quite relevant:
    • Less than a week before this sudden horn eruption I had a panic alarm go off randomly (it never happened before). The car was off and parked overnight. Pushing a keyfob button fixed the honking, so I thought nothing of it at the time.
    • Couple of days ago the passenger side low beam bulb died. Quite odd, considering it was a LED conversion kit (just like all other headlight bulbs in my car), less than a year old. Replaced it with a regular bulb, seems to be working fine.
    • High beams flicker only when the low beams are on.
    • I do have an OBDII reader… no error codes.
    • As I was visually checking the wiring harnesses for any signs of molten or burned plastic, I've removed upper and lower trim from the steering column. After putting it back together, I found a spring on the floor. Spring looks like the one in a classic clothespin, but with a very short (approx. 2mm) straight legs. Not sure if it fell from the steering wheel assy or I brought it in my shoe soles somehow.
     
  2. bisco

    bisco cookie crumbler

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    welcome!

    possible rodent damage to wiring somewhere?
     
  3. Usle

    Usle Member

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    Are there any signs of mice, on the floors, in the rear, in the cabin air filter, those nasty little suckers can cause havoc. Had the vehicle ever been flooded or in an accident?
    A Toyota dealer reading the OBD2 port might be a good idea, or even any auto parts dealer would be a good start.
     
  4. schmuber

    schmuber Member

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    Thanks, and sorry for double posting. It's in the South, so rodent damage is always an option. Or maybe even ants.

    I have a reader with Toyota-specific codec. No errors whatsoever.
     
  5. schmuber

    schmuber Member

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    Just wanted to update the post, but it won't let me… so here I am, commenting on my own post.

    The problem was fixed by replacing a combination relay.
     
    Robert Holt, jerrymildred and bisco like this.
  6. bisco

    bisco cookie crumbler

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    good news, well done!(y)
     
  7. NutzAboutBolts

    NutzAboutBolts Senior Member

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    Sounds about right with the relay.
     
  8. schmuber

    schmuber Member

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    Glad to get an approval from the Guru himself :D

    Any ideas about my new issue?
     
    NutzAboutBolts likes this.
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