electrical issue with stop lights

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

Page 2 of 2
  1. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    25,574
    16,713
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    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

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    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

    Joined:
    Mar 30, 2008
    25,574
    16,713
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    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

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    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
  5. ilya980

    ilya980 Junior Member

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    Took the car apart to get to the A41 skid ECU connector. It was very dirty on the outside, but no visible damage. Unplugged it. Lights went off. Cleaned a bit the outside part. Plugged back in. Lights flickered for a few seconds and then came back on steady. Unplugged it again a couple of times, the lights go out with connector unplugged, but are always steady on with connector plugged in. Looked closely at the wires mentioned above (3, 6,33). Wiggled them a bit. Nothing. No visible damage to any of the wires.

    Took the right front ABS sensor out from the hub. The sensor itself looked good. No visible wear at all. Dash lights and C1464 are on again. Wanted to disconnect the sensor under the cover in the wheel well but could not unlock the connector.

    I am out of ideas.
     
    #25 ilya980, Mar 1, 2025 at 5:54 PM
  6. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    25,574
    16,713
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Your c, I take it, has the brake ECU combined with the brake actuator, same way the liftback and the v do?

    The ECU may have joined the choir invisible. There has been a similar failure commonly reported for liftbacks and v wagons, only there it is usually the HZRI hazard-switch connection that goes wonky. Although intended as an ECU input, it triggers the hazards when it goes wonky. Amusingly, the usual syndrome is it makes the hazards flash faster the faster you drive.

    This might be my first time hearing of something similar in a c, and my first time hearing it involving the stop lights instead of the hazards. But it certainly sounds as if you have tracked it down to ECU internals.
     
    #26 ChapmanF, Mar 1, 2025 at 6:32 PM
  7. ilya980

    ilya980 Junior Member

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    How can I confirm it is a skid ECU before committing to a difficult and expensive repair? Yes, combined ECU and actuator. Is there a procedure to test pins on the A41 connector and confirm that, at least, relevant pins 3,6,and 33 are not shorted to something else?

    Also, is there a close up on how to disconnect right front speed sensor on a prius c? It is under a wheel well cover that I can't remove, difficult to reach and see, attached to the metal frame. I can't see where the lock is and how to unlock it.

    Thanks.
     
    #27 ilya980, Mar 1, 2025 at 8:20 PM
  8. ilya980

    ilya980 Junior Member

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    Here are a few photos of the connector
     

    Attached Files:

    #28 ilya980, Mar 1, 2025 at 8:25 PM
  9. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    25,574
    16,713
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    If you've confirmed the problem is present when the wiring is connected to the ECU, and not present when it isn't, I'm not sure how much more testing would be practical or useful.
     
    #29 ChapmanF, Mar 1, 2025 at 10:12 PM
  10. ilya980

    ilya980 Junior Member

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    If the wiring is short, and both wires are not powered while disconnected, it can create a problem when connected, if a signal from ECU should go through one wire and not another. But the ECU might be fine.
     
    #30 ilya980, Mar 1, 2025 at 10:50 PM
  11. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    25,574
    16,713
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    #31 ChapmanF, Mar 1, 2025 at 10:53 PM
  12. MAX2

    MAX2 Active Member

    Joined:
    Aug 12, 2024
    744
    217
    46
    Location:
    Third planet from the Sun
    Vehicle:
    2007 Prius
    Model:
    N/A
    Check the wiring again.

    Also, you still haven't explained why you thought the relay was faulty and replaced it.

    It happens that the replaced part does not solve the problem because it itself is problematic.

    The check procedure is as follows.
    INSPECT STOP LIGHT SWITCH ASSEMBLY (for LED Type Stop Light)
    1. Disconnect the connector from the stop light switch assembly.
    2. Measure the voltage according to the value(s) in the table below.
    Standard Voltage
    Tester Connection Switch Condition Specified Condition
    7 (B) -2 (GND) Ignition switch off 11 to 14 V
    6 (B) - 2 (GND) Ignition switch ON (IG) 11 to 14 V

    • Measure the resistance according to the value(s) in the table below.
    Standard Resistance
    Tester Connection Switch Condition Specified Condition
    2 (GND) - Body ground Always Below 1 Ω

    • Reconnect the connector to the stop light switch assembly.
    • Measure the voltage according to the value(s) in the table below.
    Standard Voltage
    Tester Connection Switch Condition Specified Condition
    1 (OUT) -2 (GND) Ignition switch off, brake pedal not depressed Below 1 V
    1 (OUT) -2 (GND) Ignition switch off, brake pedal depressed 11 to 14 V
    3 (L) -2 (GND) Ignition switch off, brake pedal not depressed Below 1 V
    3 (L) -2 (GND) Ignition switch off, brake pedal depressed 11 to 14 V
    5 (L) -2 (GND) Ignition switch ON (IG), brake pedal not depressed 11 to 14 V
    5 (L) -2 (GND) Ignition switch ON (IG), brake pedal depressed Below 1 V
    4 (ACC) -2 (GND) Ignition switch off 11 to 14 V

    If the result is not as specified, replace the stop light switch assembly.
     
    #32 MAX2, Mar 1, 2025 at 11:36 PM
  13. ilya980

    ilya980 Junior Member

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    The car died today in the morning. I drove it yesterday. Parked it. Today in the morning before starting the car I heard rapid clicking from a relay. The picture is attached. The car looks completely dead. I pulled it out. Clicking stopped, but if I put it back in clicking continues.

    The diagram says it is a DOME CUT.
     

    Attached Files:

    #33 ilya980, Mar 2, 2025 at 2:47 PM
    Last edited: Mar 2, 2025 at 3:00 PM
  14. ilya980

    ilya980 Junior Member

    Joined:
    Nov 3, 2020
    61
    10
    0
    Location:
    Massachusetts, USA
    Vehicle:
    2013 Prius c
    Model:
    One
    12 V battery was causing all problems. Hooked up a battery from another car. Everything is fine, no lights. Speed sensor lights are still on, but that is ok for now. I hope I don't have a short somewhere that drains the battery...

    Update: stop lights are back on with ignition off :( They key again does not work. This is with another 12V battery hooked up with jumper cables, with OEM 12V battery removed. The OEM battery when removed today showed 9.4V.

    I am measuring 0.45A parasitic current with the STOP fuse removed. It is a lot. How do I find what is causing the current? Is there a diagnostic procedure to track it?

    Thanks.
     
    #34 ilya980, Mar 2, 2025 at 3:26 PM
    Last edited: Mar 2, 2025 at 6:14 PM
  15. MAX2

    MAX2 Active Member

    Joined:
    Aug 12, 2024
    744
    217
    46
    Location:
    Third planet from the Sun
    Vehicle:
    2007 Prius
    Model:
    N/A
    The source of the parasitic leak is found by successively removing the fuses until the leak stops.

    But you need to remember about the "sleep" period of the various systems of the car.

    The car must be closed, otherwise the ECU will not sleep.
     
    #35 MAX2, Mar 2, 2025 at 11:03 PM
(You must log in or sign up to post here.)
Page 2 of 2