Horn Not Working (Driver-side)

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by blaze001, Mar 15, 2021.

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  1. blaze001

    blaze001 New Member

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    2010 Prius III_Horn disconnected.jpg

    Hey everyone,

    I'm trying to troubleshoot a horn issue I'm experiencing on my 2010 Toyota Prius III. The passenger-side horn is working and activates when panic button is pressed, however, the horn on driver-side does not work when steering wheel is pressed down. All other buttons on steering wheel work just fine.

    I purchased a new horn and followed a YouTube tutorial on its replacement, but this did not resolve the main issue. Using a multimeter, I can see that voltage is not coming through connector circled in red. (The one on the left works just fine.)

    I'm an amateur when it comes to car mechanics so any advice on how best to troubleshoot and proceed would be appreciated.

    TIA!
     
  2. tankyuong

    tankyuong Senior Member

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    Broken clockspring
     
  3. ChapmanF

    ChapmanF Senior Member

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    I do not think the clockspring (a/k/a spiral cable) has separate circuits for the left and right horns.

    Whether a person is an amateur or a pro when it comes to car mechanics, the first stop is the same: the wiring diagram.

    horn.png

    That way, you see that there is indeed only one steering pad horn switch and it only follows one wire through the spiral cable to the integration relay. So if there were a spiral cable problem, there would be either both horns or no horns.

    You then also see that each horn is wired directly back to its own output from the integration relay. So your troubleshooting doesn't have very many things you need to check. Continuity of that black wire from the horn connector A3 back to pin 6 of connector 1G at the integration relay. If that's ok then it might be the integration relay itself. Do you have a multimeter? (Edit: you do, I see you said that.)

    1G6.png

    Of course connector 1G is on the side of the integration relay you can't see from the top. The relay should be removable out through the top of the fusebox, but I've never done it, and I don't know whether there's enough slack on the 1G, 1H, 1I connectors to get it all the way out through the top, or if you need to get the fusebox loose and work through the bottom (ugh).
     
    #3 ChapmanF, Mar 15, 2021
    Last edited: Mar 15, 2021
  4. blaze001

    blaze001 New Member

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    Wow, thank YOU! for the detailed response and for providing the wiring diagram and relay diagram. The logic makes complete sense, and it’s helped me realize that I’ve reached an impasse being that I’m unable to get the relay out on my own (not enough slack) to check on the 1G pins. I’ve scheduled an appointment for the dealership to take over the investigation and hopefully resolve this. If I didn’t have need of the car, I could’ve kept tinkering with it.

    Thanks again for the valuable insight. I’m glad to have stumbled upon such a helpful community devoted to the Prius in my troubleshooting quest.

    I will post an update on how this issue gets resolved, to help others who also may encounter this issue in the future, and to also close the loop on this thread.
     
  5. blaze001

    blaze001 New Member

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    Just to follow up, the dealership said it was both the spiral cable and the integration relay that failed. Charged 1k for the fixes smh.
     
  6. sam spade 2

    sam spade 2 Senior Member

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    Two comments about that:
    You apparently did not read the previous excellent diagnosis of the problem posted here.......which indicated that the clock spring/spiral cable can NOT be the cause of the stated problem.
    Then......you spent $1000 just to fix one of the two horns.....on a 10 year old car ???? REALLY ??? :eek:

    You could have done a $20 "work around" by replacing the one working horn with a louder one.
     
  7. ChapmanF

    ChapmanF Senior Member

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    If I had to guess, I'd guess the dealer changed the spiral cable pretty much by reflex, then realized that hadn't solved the problem, then figured out what the problem was, then just said it was both.
     
  8. blaze001

    blaze001 New Member

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    They replaced the Integration Relay first and issue was not resolved. (I verified the horn was not working after solely replacing the IR.)
    It was only after replacing both IR and clockspring that horn finally worked.

    Replacing the one working horn with a louder one wouldn't be of any use to me since that horn only works when panic button is pressed.

    Re: the comment about money. Time is greater to me than $$. To each his own, though.

    All the best, gentlemen.
     
  9. Fernando12355

    Fernando12355 New Member

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    Well, I am not sure if you have the same issue I had. I was installing an aftermarket alarm system and I noticed the driver side horn did not function with the push button on the steering wheel. Turned out. It only works with the alarm system. The passenger side is the only one that works with the steering wheel button. But both work with the panic button or probably if the anti theft system is triggered
     
  10. ChapmanF

    ChapmanF Senior Member

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    Are you working on a 2006 Gen 2 (according to your profile) or a Gen 3 (as you've posted in the Gen 3 forum).

    On my Gen 3 with the stock wiring, both horns definitely sound together when the steering wheel pad is pressed, just as the manual says. I'm pretty sure Gen 2 is the same way, but I don't have one of those in the driveway, so I'll have to crack that manual and look.

    (While you're waiting, press 1 to order a box of delicious PriusChat caramel corn....)

    Yup - Gen 2 also has a high-pitch and a low-pitch horn mounted behind the grille, wired back to a single output of a single horn relay, so if there has been no damage and no wiring mods, they both will sound when you press the steering wheel pad. If yours behave differently now, that could be a consequence of how the alarm was installed. I would probably try to install it in a way that would not change that behavior.

    The wires in Gen 2 are both black, they join at junction connector J2, and then it's just one single black wire back to the horn relay, connector 3J pin 8. (These specifics are from a 2006 book.)

    Just to keep things interesting, it appears possible in some world markets for both Gen 2 and Gen 3 to have a third horn, specifically for an alarm system. The Gen 2 manual even shows where the third one goes (way back by the firewall, right side of car, where it's hard to thwart, not out in front at all). The wire to that one is yellow, controlled by the body ECU connector B6 pin 1.

    Maybe all gen 2s have that? For Gen 3, it doesn't seem to be standard in the US, but you can still find traces of it, like an unused "S/HORN" (security horn) fuse position in the fuse box. I'm not sure which markets include it.

    Responding belatedly to post #8, the way that problem was originally reported (one of the front horns would sound and the other would not, when the steering pad was pressed), a quick look at the wiring diagram in #3 is enough to see that the clockspring was ruled out, as in not at all possible as a cause of that issue ... which means if the events in #8 happened as described, the shop must have created a new problem (perhaps inadvertently) when they replaced the integration relay, and then eventually figured it out when they went back and fussed with the clockspring. Stuff like that happens sometimes.
     
  11. Fernando12355

    Fernando12355 New Member

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    I have owned many gen 2 and currently own a gen 2 and one 2015 gen 3. It was on the gen 3 that I noticed that. I thought it was a bad connector since only one horn works I even swapped grounds and the connectors.only right one goes off with button but if right one is disconnected. Left one works. The only way to get both to go off is with panic button on remote. Makes sense to be honest.
     
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