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Help! Brake light intermittently working

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PaulD76, Dec 1, 2015.

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  1. PaulD76

    PaulD76 Junior Member

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    My passenger side brake light has developed a fault over the past couple of months.

    The brake light will work, for example, when I turn the car on both lights will come on, however if I then take my foot off the brake and re-apply it, it will not work. However later when I am driving I will notice (via reflections) that it is working again!

    I am aware that the bulbs cannot be replace and that I would need to replace the whole unit (after market versions available for £75 ish).

    I have attempted to check the cabling and everything appears OK but I am not an expert. I just removed the rear panelling and made sure nothing was loosely connected.

    More than happy to replace the unit but something doesn't seem to make sense (if the bulbs are gone how come they do work on a repeatable sequence). Not keen to take to Toyota as suspect they would just want to replace the light as first choice.

    Thanks if anyone can shed any 'light' (oops sorry) on this annoying issue. MOT in JAN so keen to fix now! :D
    Thanks!
    Paul
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Find the wiring harness leading to the rear tail light assemblies, and look for a place where wires are bolted to body ground. You probably have to remove the trim around the bottom of the hatch opening which you can do just by pulling up on the plastic. Make sure the connections to body ground are tight.

    You can also remove and replace the wiring harness connector to the passenger-side tail light assembly. If you see any corrosion within the wiring harness connectors, use electrical parts cleaner spray to clean that out.
     
  3. PaulD76

    PaulD76 Junior Member

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    Thanks Patrick - I will give this ago tonight. Want to try everything before I go to Toyota! :)
     
  4. PaulD76

    PaulD76 Junior Member

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    Hi Patrick

    I took a look at all the cables around the light unit and generally around the boot area, and everything looked fine with no sign of corrosion or being lose. All the ground bolts seemed tight.

    I did notice tonight however that the brake light is now working but very faint and flickering. I have read other threads and seen this has been resolved by replacing the light unit, so this makes me more confidence to take this approach.

    My big fear is to fit a new light unit and find the problem is still there, but now I feel 75% hopeful a new unit will fix the problem.

    Thanks
     
  5. bisco

    bisco cookie crumbler

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    can you find a salvage unit?
     
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Well, if you have a digital multimeter you potentially could back probe the wiring harness connector to make sure that 12V is present at the brake light terminal as a helper depresses the brake pedal for you. Compare to the light wiring harness connector on the other side of the car.
     
  7. PaulD76

    PaulD76 Junior Member

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    Hi Bisco - I have been able to find a replacement unit online for £65 which is very reasonable. I did look at the local breakers yard but sadly nothing..

    Hi Patrick - Sadly I do not have a multimeter but I will try to pick one up. What confuses me is that the other lights on that unit work with no issue. If the brake lights are LED, I would assume they don't need much power? I would have thought if any of the lights work its most likely not a volt problem (but I could be completely wrong!). Last night my wife stood behind the car (plus I purposely parked in front of a glass window) and the lights very very faint... some of them would flicker on and off..

    Thanks again for all the tips and suggestions!
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Most likely the tail light assembly (which includes the LED brake lights) has failed. However if you want to be sure, measure the voltage for the brake lights.
     
  9. PaulD76

    PaulD76 Junior Member

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    Thanks Patrick. I just ordered a replacement light for a good price, £65 (about $98) and it will arrive on Wednesday.. I can return it if i need to.. Will let you all know. The lights do not come on AT ALL now, so i feel they just started to fail and slowly went from partial to complete failure!! Appreciate all your knowledge and willingness to share it :D
     
  10. PaulD76

    PaulD76 Junior Member

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    Great news! Light turned up today.. was easily able to remove the old unit and fit the new unit... new light works as new so very happy! :D Thanks again
     
  11. tnt01prius

    tnt01prius Member

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    Glad it worked out for you. I'm seeing same problems with the passenger side LED brake light: out, dim, bright cycles. With brake depressed these LEDs are heating up making the lens very warm, when the LEDs are dim. Seeing just slightly lower than 12V at the harness connector on both sides. Drivers side LEDs are bright. I haven't found any wiring issues. So, I will replace the unit. I did notice most units on ebay are new aftermarket and a few used OEM. Has anybody had good experience with aftermarket tail lights?