1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Hazard Lights Problem Debug Info

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by xywang84, Apr 5, 2019.

  1. xywang84

    xywang84 Junior Member

    Joined:
    Apr 5, 2019
    5
    3
    0
    Location:
    Watertown, MA
    Vehicle:
    2010 Prius
    Model:
    II
    Hey guys,

    I've also encountered the Hazard lights going crazy (blinking extremely fast) while driving problem in my 2010 Prius. In addition, my hazard lights do not turn off when parked except by either pulling the flasher control relay or the Turn Signals and Hazards fuse. In this state, it flashes at a normal rate. I have spent some time debugging this issue and I wanted to share some insights that I have gained. Even though the problem hasn't been fixed, I hope having more information out there can be useful to some people.

    From looking at the 2010 prius wiring diagram Pg. 65 (attached), it appears there are three signals that drive the L55 harness HAZ pin (pin 8), which are all connected through Junction Block 3A and 3B. these are the hazard switch, the Main Body ECU and the Skid Control ECU. When I drive the problem is intermittent, so pressing the hazard button while the problem is not occurring actually triggers the hazards appropriately. This means that the grounding mechanism of the switch is working as usual, and also indicates that applying ground to pin 8 is what causes the hazards to blink.

    Additionally, using masking tape on Pin 8 to prevent the connection to the L55 HAZ pin solves the flashing-while-driving and flashing-while parked issues, but prevents hazards from ever getting switched on.
    This is a temporary solution, but will not pass inspection.

    I would like to debug this further, but I would like to get some help as to where Junction Block 3A and 3B are located in the 2010 Prius. I found a 2006 Prius manual that gives locations of the Junction Blocks, but I couldn't find similar information for the 2010. My current hypothesis is that either the Main Body ECU or Skid Control ECU are driving the hazards to ground erroneously. When parked, there is a short-to-ground condition and while driving it would seem like there is a PWM-ish signal. In fact, sometimes while parked the rapid-flashing state would occur, which means that whatever is driving this signal is active even when IGN and ACC relays are off. The other possibility is that the harness has developed a short somewhere. I would love to hear the opinions of people on this forum about what could be the issue.
     

    Attached Files:

  2. tankyuong

    tankyuong Senior Member

    Joined:
    Nov 9, 2012
    1,555
    661
    0
    Location:
    Central MO
    Vehicle:
    2012 Prius c
    Model:
    II
    Check your 12v battery
     
    AzWxGuy likes this.
  3. gscotten

    gscotten New Member

    Joined:
    Jun 26, 2021
    5
    0
    0
    Location:
    USA
    Vehicle:
    2012 Prius
    Model:
    III
    I have the same problem, and sure would like to know where the Junction Block 3A and 3B is. The manual shows the layout, and I figured anything with that many pins would be easy to find. I have the dash out and don't see anything that looks like it. The manual often refers to checking voltages and/or continuity between pins on it, so it must be fairly easy to get at. Anybody have an idea?
     
  4. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,984
    16,274
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Easy for you, if you've already got the dash out! You should see it mounted there on the reinforcement, slightly to the left of the center stack. Doesn't look like much, just a rectangularish box that has the 3A and 3B connectors from the harness plugged into it. It just has internal patterns that connect various of the pins together, as an alternative to a whole lot of wire splices.

    You might want to look at this post. The behavior where the hazards flash at a rate that increases with road speed really sounds to me like a short between HZRI and the "speed pulse" signal SP1, which is generated by the brake ECU on the next pin over (and there really isn't anything else it sounds like that I can think of).

    There's also another member currently looking at a (different, but) possibly related situation.
     
    #4 ChapmanF, Jun 26, 2021
    Last edited: Jun 26, 2021
  5. gscotten

    gscotten New Member

    Joined:
    Jun 26, 2021
    5
    0
    0
    Location:
    USA
    Vehicle:
    2012 Prius
    Model:
    III
    Thanks. According to the wiring diagram there are three inputs to the flasher module that are joined together at the junction block. I figure that is the best place to figure out where the ground is coming from. Here is a picture. Is it in the box under the green and orange cables? Nothing looks like the diagram in the manual. The dash actually came out pretty easy. Having done it once, I could probably do it again in 10-15 minutes. IMG_1525.JPG
     
  6. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,984
    16,274
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Looks like you've only removed the upper dash, lazybones.

    The box you're looking at there is the power steering ECU. If it were gone you might see a bit more of the JB No. 3 in the photo. It's a bit to the right, closer to the midline of the car. It is mounted to the reinforcement (that big round metal pipe thing).

    I remember spotting it when I had my dash off, but I didn't take photos, sorry.

    Because the usual symptoms give a clear suggestion of where the grounding is happening, if it ever happened to me I think HZRI / SP1 is where I would focus first. In the diagram, of course, JB No. 3 makes a perfectly logical place to divide and conquer the problem, but in physical layout, as you see, it's not convenient.

    Edit: was sure I had to have this diagram somewhere. As you can see, when you're looking at the steering ECU, you're getting pretty warm.

    inr.png

    It turns out when you download from the online wiring diagram manual, this diagram ends up in the PDF for engine compartment relay locations, which is why I thought I was losing it for a minute there.

    Looking things up is really easier when you're signed in to the online diagram, and then you just highlight circuits with the mouse and click Info and boom, you see where all the bits are.
     
    #6 ChapmanF, Jun 27, 2021
    Last edited: Jun 27, 2021
  7. gscotten

    gscotten New Member

    Joined:
    Jun 26, 2021
    5
    0
    0
    Location:
    USA
    Vehicle:
    2012 Prius
    Model:
    III
    Thanks! You've really been a big help. I agree that the logical cause of the trouble is in the ABS unit, but I thought that the junction blocks would be easier to access. The service manual refers to taking measurements from the 3A and 3B junction blocks in most of the trouble shooting steps for most of the various circuits in the car.. I figured Toyota had placed them where they would be convenient for their techs. Wrong again.

    My diagram shows your junction blocks as CAN J/B 3 and 4, and they appear to be way smaller than J/B 3A and 3B should be, having 84 and 96 pins each. Hope you can see why I was confused. And I can't even find anything in those areas that resemble the diagram in the manual. It is such a simple circuit that I figured this would be easy. It would be if I could find anything. [Sigh] There is just too much I don't know about this.....

    The resistance to ground at pin 8 of the flasher is supposed to be >10k, and it shows 280k, so I suspect the short in the ABS must be internal and active. Not looking forward to figuring out how to get to that to check it. :(

    Thanks again for all your help!

    George
     
  8. gscotten

    gscotten New Member

    Joined:
    Jun 26, 2021
    5
    0
    0
    Location:
    USA
    Vehicle:
    2012 Prius
    Model:
    III
    The problem certainly is originating inside the ABS unit. I fixed it by adding an air gap to the wire. :) Now everything is working except my flashers will no longer flash when I am skidding. (That has never yet happened.)
     
  9. Mick Gilluley

    Mick Gilluley Junior Member

    Joined:
    Sep 23, 2013
    1
    0
    0
    Vehicle:
    2010 Prius
    Model:
    Three

    hi there like a few others i to am having this issue ,,, can you advise please which wire you cut to stop the signal being sent to the flasher unit if skidding, lets face i your brake lights will be on anyways, ??
     
  10. gscotten

    gscotten New Member

    Joined:
    Jun 26, 2021
    5
    0
    0
    Location:
    USA
    Vehicle:
    2012 Prius
    Model:
    III
    Pin 4 of junction block 3B. But I would not do that again. Spice a new wire from the yellow wire on the flasher switch to pin 8 of the flasher unit. Means the flashers won't flash when you unlock the car or hit the panic switch on the fob, but it will save you an hour or more of work getting to the j/b. A complete description is on this forum.
     
  11. imran Arshad

    imran Arshad Junior Member

    Joined:
    Sep 2, 2020
    9
    1
    0
    Location:
    New york
    Vehicle:
    2007 Prius
    Model:
    Limited
    clean the ecu connector under the hood and change the hazards relay which is under the steering then it will be fixed.
     
  12. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,984
    16,274
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    That may have worked for someone for some reason, but as a recommendation that'll be dubious unless someone pins down what was at fault and how, and can make that explanation fit with the already-gathered evidence.

    It is true that the HZRI and SP1 pins are right next to each other at the brake ECU connector,

    [​IMG]

    However, when a member with the problem investigated, the connector and terminals were pristine inside.

    That would be the thread to continue on with further exploration. As far as I know, no one has yet obtained a unit with the problem and disassembled it for further exploration inside. That would be a sensible next step.