electrical issue with stop lights

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by ilya980, Feb 25, 2025 at 10:04 PM.

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  1. ChapmanF

    ChapmanF Senior Member

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    If this is a 2013 Prius c, the wiring may be somewhat similar to the gen 3 liftback, which has an item called the stop light "relay", which is really more of an electronic thing than a relay, and it has multiple inputs, including from the pedal switch and one from the skid ECU so it can light the stop lights when slowing for other reasons.

    If I remember right, the Prius v (which is also kinda-like a gen 3) is wired similarly, but the discrete stop light "relay" went away and got integrated into, of all things, the combination meter? Maybe the c is like that too, as the c and v both appeared a couple years after the OG gen 3 liftback.

    Anyway. The wiring is interesting enough that you probably will want to be looking at the wiring diagrams first-hand.

    Toyota Service Information and Where To Find It | PriusChat
     
    #21 ChapmanF, Feb 28, 2025 at 11:23 AM
  2. ilya980

    ilya980 Junior Member

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    I have 2013 Prius C one, not V. There are some similarities with Gen 3.

    You were leading the thread I mentioned on Gen 3 a few years ago. Was the issue resolved? What was the problem?

    I scanned all ECUs today with Techstream and got only one active C1464 (right front speed sensor). The OP in Gen3 thread mentioned same thing. Coincidence? Maybe... Would be nice to know what the problem was. Can a shorted speed sensor cause these problems?

    I cleared the code. Drove the car around with Techstream running and looked at wheel speeds. Everything seems normal. All 4 speeds are the same and match the speed of the car. No lights on the dash.

    I checked the 12V battery. Did the recommended test with ignition off, 30 seconds high beam on, and the voltage was 12.2V. The manual says above 12V is normal.

    The stop lights turn off if the car is either running, or ignition is in the "ON" position. With the ignition "OFF", the lights stay on and never blink.

    No evidence of rodents under the hood. Everything is pristine inside near the brake pedal, no water damage, no dirt, etc.

    Seems difficult to get to the ECU connector. I couldn't even see it. How hard is it to get to?
     
    #22 ilya980, Feb 28, 2025 at 12:50 PM
  3. ChapmanF

    ChapmanF Senior Member

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    Sorry, I was talking about the Prius c compact and the Prius v wagon. Both came out in 2012. Neither is the same as a gen 3 Prius liftback (which you could buy in a "V" trim in the early years), but they are from roughly the same era.
     
    #23 ChapmanF, Feb 28, 2025 at 12:56 PM
  4. ilya980

    ilya980 Junior Member

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    Thank you for the diagrams. They are very helpful. The power management ECU is inside, connectors look pristine. It looks like the primary suspect is a faulty signal coming from the skid ECU, which is outside. I am going to try to reseat A41 connector. Sounds like I need to remove wipers and the grill. Time to clean the intake mesh on the grill, I guess. :)

    I am surprised there is no fault code. If skid ECU sends an erratic signal to illuminate the stop lights, it should know that the ignition is off, and the brake pedal is released.
     
    #24 ilya980, Feb 28, 2025 at 2:31 PM
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