2010 Gen Three Prius Trunk Lock Intermittent Failure

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by kleinfelter, Jul 24, 2025 at 8:58 PM.

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  1. kleinfelter

    kleinfelter Junior Member

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    Occasionally, the rear hatch doesn't unlock when I double-press the key fob unlock button. About 1 in 20 attempts.

    The car chirps, the lights flash, but the hatch won't open when I press its release button.

    Sometimes a single retry is enough. Sometimes it takes 3-4 attempts.

    I wouldn't mind replacing the actuator, but the reviews on Amazon indicate that cheap replacements can fail after 6 months. Any suggestions for diagnosing and curing the current actuator? Or a work-around?

    Using the mechanical release button isn't feasible because it usually happens when I have a trunk full of groceries!
    TIA
     
    #1 kleinfelter, Jul 24, 2025 at 8:58 PM
  2. xliderider

    xliderider Senior Member

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    Have you tried some lubrication? Also, you might want to see if something has fallen in there and is causing interference in there.
     
    #2 xliderider, Jul 24, 2025 at 9:35 PM
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  3. kleinfelter

    kleinfelter Junior Member

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    Good points.
     
    #3 kleinfelter, Jul 24, 2025 at 10:56 PM
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    What price for genuine drove you to Amazon. I’m seeing mostly $172~ CDN ($126 USD) here:

    https://www.amayama.com/en/genuine-catalogs/epc/toyota-usa/prius/ZVW30L/13501/body/6709

    see what it is with shipping for you. I’ve used them and so far shipping was the only extra, no sales tax or import duty. Do verify with your frame number or VIN.
     
    #4 Mendel Leisk, Jul 25, 2025 at 12:33 PM
    Last edited: Jul 25, 2025 at 12:40 PM
  5. ChapmanF

    ChapmanF Senior Member

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    What goes on with the hatch is different from what goes on with the doors.

    In the doors, there's a mechanical difference between locked and unlocked. The actuator physically moves from locked to unlocked when you press the fob button. Then when you pull the door handle, it opens because it's unlocked.

    The hatch is different. Its electric actuator releases right at the moment you press the hatch release button. Or it doesn't, if the Body ECU considers the hatch to be locked. There isn't anything mechanical happening to the hatch when you press the fob unlock button; the only change is the Body ECU now thinking "ok, I'm unlocked" instead of "go away, I'm locked".

    This might help with diagnosis a little, because with the doors you can have a situation where the actuator isn't always mechanically moving from locked to unlocked when you press the fob button, and that'll often be the door actuator.

    But the hatch's electric actuator operates just at the moment you release the hatch, every time. Of course it should never, ever open when the body ECU considers the hatch locked, and it should open on every attempt when the ECU considers it unlocked.

    In a state where you know the ECU considers the car unlocked (this is probably in the viewable live data), if the hatch doesn't open reliably every time you press the hatch release, that could be an actuator problem. But if the symptoms seem more as if the ECU isn't always going to unlocked state when you use the fob button, the issue is more likely in the wireless key system.
     
    #5 ChapmanF, Jul 25, 2025 at 1:31 PM
  6. kleinfelter

    kleinfelter Junior Member

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    Very helpful @ChapmanF. So it could be a problem with either the unlocking system, or with the unlatching system that only APPEARS to be related to the unlocking system because I seldom try to unlatch it except when I've just unlocked it.

    It looks like the diagnostic steps are:
    1. Next time it happens, see if the unlock switch in the driver door will "unlock" the hatch. Need to test this on multiple occasions to rule out coincidentally moving past an intermittent unlatching issue.
    2. If the driver door unlock switch really does work, then I forget about repair because I can live with unlocking it that way.
    3. If the driver door unlock switch does NOT resolve the issue, the problem is either in the switch or the solenoid. I don't see a way to diagnose which of those is the problem except to replace one. I'll probably replace the switch because it looks easier.
    If it ever goes to a 100% failure rate, it gets easier to diagnose.

    Anyone know if the switch in the hatch door is normally open or normally closed? If the failure rate goes to 100% and the switch is normally open, I can pull the switch, short the contacts, and listen for the unlatch solenoid. And/or I could operate the manual hatch unlatch, and then poke at the switch and listen for the unlatch solenoid.
     
    #6 kleinfelter, Jul 26, 2025 at 5:42 PM
  7. kleinfelter

    kleinfelter Junior Member

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    @Mendel Leisk - I looked at Toyota, saw $475 and went to Amazon. For simple stuff, I've had pretty good results with Amazon. There's something that feels dodgy about the vendors selling this part on Amazon because none of them has more than a few reviews. Or maybe that's a sign that the solenoid seldom fails.
     
    #7 kleinfelter, Jul 26, 2025 at 5:48 PM
  8. ChapmanF

    ChapmanF Senior Member

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    The switch in the hatch does not, of course, directly control the latch actuator.

    The switch is just an input wired back to an ECU. An ECU then sends power to the actuator, if the the car is considered to be unlocked, or does nothing, if the car is considered locked.

    The pushbutton, like a lot of simple inputs, is just a normally-open switch that pulls one wire to ground when you press it. In cars with just the driver-door-only smart-key system, the switch is wired straight to the body ECU. In cars with the all-doors smart-key system, the hatch switch is wired to the certification ECU, which communicates over CAN to the body ECU. The body ECU is what sends power to the actuator.

    I think the actuator is like the ones in the doors, a motorized worm-gear operation, rather than a solenoid.
     
    #8 ChapmanF, Jul 26, 2025 at 8:58 PM
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