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Gen 3 Prius V - Hazards won't turn off

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by Danno M, Oct 20, 2024 at 3:17 PM.

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  1. Danno M

    Danno M New Member

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    Location:
    Eastern MA
    Vehicle:
    2013 Prius v wagon
    Model:
    Five
    The Lead Up:
    A few months ago, my 2013 Prius V with ~138K miles started to throw some errors where some of the lights on the dash went on indicating issues with the ABS system. I took a picture of them but I can't for the life of me find it right now. I think it was the lights for the Brake, Traction Control, ABS and a few others. The lights would come on and within 5-30 minutes would usually go away again.

    The Problem:
    About a month ago I walked up to my car after a quick stop, and noticed my hazards flash very quickly (<1 second) and turn off again. When I got in the car, nothing seemed to be amiss and the rest of the day went normally. The next morning, after another momentary stop, I came back to the car and the hazards were on. Since then, the hazards have never turned off.

    I need to fix this problem within two months because I live in MA, and as part of the yearly safety inspection, all cars on the road must have functional turn signals and hazards, and my tag is due this month (they apparently allow a 60 day window).

    What I've Tried:
    I took it to a local shop who said that they thought that it was an issue with a relay in the dash, but that they couldn't get the dealership to get them the part and that I'd have to take it to the dealer. Thinking that this was a bit weird, I did a tiny bit of debug myself. I pulled the hazard switch from the dash and disconnected the cable and it made no difference. I pulled some relays and fuses hoping that I could isolate the fault by system, but no luck. The best compromise I've made is to just pull the fuse for the turn signals and the hazards. I still get the constant clicking (even with the car off) but at least people on the road aren't confused.

    I took it to the dealer who diagnosed the car with several faults:
    • C1239 Foreign Object is Attached on Tip of Rear Speed Sensor LH
    • C1466 Rear Speed Sensor RH Circuit
    • C1467 Rear Speed Sensor LH Circuit
    Additionally they said that the fault causing the issue with the hazards was inside the ABS ECU as part of the ABS Brake Booster Assembly, and their solution would be to replace the whole assembly. In total they quoted $3k for the Brake Booster replacement and $1k for each rear wheel to replace the rear wheel hub and bearing assemblies.

    I took the car home because I didn't want to pay them damn near the total value of the vehicle. I replaced the rear wheel hub and bearing assemblies myself because I'm at least moderately handy.

    Finally, I got into the engine compartment and did a little fiddling. I found interestingly that unplugging the harness from the ABS actuator did not clear the condition. While I was in there I lightly scoured some of the contacts on the Brake Booster side of the connection in case there was corrosion making a problem, but that didn't help either. If the fault is caused by a short inside the Brake ECU pulling a signal to ground, like the dealership claimed, I would think that it's possible that unplugging the connection would clear the faulty condition. Because unplugging it didn't stop the hazards, it leads me to think that the short could be somewhere else like inside the harness.

    Final Thoughts:
    Do any of you have any suggestions on what I could try next to debug the system? It would be quite nice if I could do enough debugging myself to isolate the issue before I commit to spending $3k for the Brake Booster replacement if that's what it is. Thank you so much for reading this long post!
     
    #1 Danno M, Oct 20, 2024 at 3:17 PM
  2. rjparker

    rjparker Tu Humilde Sirviente

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    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Did the speed sensor problems clear?

    The brake booster is a known issue but I would expect different codes mandating its replacement. They did not have other codes to support the brake booster replacement?

    The flasher ic circuit is in the combination meter. In a v the combo meter is reliable.

    First thing I would do is load check the 12v battery. They have been known to cause odd issues.

    IMG_6464.jpeg IMG_6465.jpeg
     
    #2 rjparker, Oct 20, 2024 at 8:16 PM
  3. ChapmanF

    ChapmanF Senior Member

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    Location:
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    Vehicle:
    2010 Prius
    Model:
    IV
    rjparker's 2nd illustration shows a yellow wire from L27 pin 4 at the combination meter, wandering off toward the Hazard Warning Signal Switch Assembly.

    The illustration above it shows the Hazard Warning Signal Switch Assembly, but no yellow wire arriving there. This actually isn't unusual in the Toyota wiring diagrams: they'll have one diagram show a certain thing, but only the parts of it that matter for that one diagram's purposes. That one drawing is showing only the trip odometer, clock setting, and MPH/km/h buttons (which apparently are included in the Hazard Warning Signal Switch Assembly, in a v).

    Elsewhere in the EWD, there is probably another picture of the Hazard Warning Signal Switch Assembly that won't show the odometer and clock buttons, but will show the hazard switch, and will show the mystery wire arriving there.

    I'll guess, though, that the real story will be in where else that mystery wire goes, on the way. In the liftback, it turned out there's a splice in that wire and it also connects to a terminal HZRI on the brake actuator (for reasons no one has ever quite explained).

    I believe the v brake actuator is similar to the gen 3 liftback's, and if it turns out there is also a connection from it to the hazard switch, I would give it a suspicious eye.

    There have been a lot of cases of that brake actuator terminal getting shorted to something internally there, and causing the hazards to misbehave. If it gets shorted to ground, it'll just make the hazards be on all the time. If it gets shorted to the SP1 speed-pulse signal (which is the terminal right next to it), you get an even goofier effect, where the hazards flash faster when the car is going faster.

    Now that I've written all that, for the first time I notice your post #1 mentions you unplugged the brake actuator and the hazards were still on. :oops: So i would say you probably have ruled out a short inside the actuator.

    That being the case, you probably are going to want to look at enough of the Electrical Wiring Diagram to find all the places that hazard switch wire gets spliced off to. The thread I linked above has illustrations showing details for the liftback, but they could be different for the v.

    Toyota Service Information and Where To Find It | PriusChat

    Once you know the whole path of that signal, you can break out a meter and start figuring where it is being pulled to ground.

    In the liftback, it goes through at least one junction connector, which at least offers you an easy opportunity to break it there and find out which side is pulled down. (Or, it would be an easy opportunity, if the junction connector was easy to get to.)
     
    #3 ChapmanF, Oct 20, 2024 at 9:53 PM
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