code p3102 and intermittent triangle of DOOM

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by dogChair, Jul 3, 2026 at 4:03 PM.

  1. dogChair

    dogChair New Member

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    hey gang. I've been combing through old threads and decided to finally just post my own issue.
    I've got a 2008 prius that's bounced back and forth from the shop for a week now. Initial issue was it refused to go into drive or reverse and had the '!' triangle.
    The car will start with all its warning lights on, parking button light blinking, and won't shift into drive or reverse.
    The most consistent trouble code my bluetooth obdII checker reads is p3102 but it occasionally throws other ones. It threw P1116 the other day then hasn't thrown it since. The only thing I can think of that was different was today it's hot (I live in Florida) and two days ago when it threw p1116 it was raining and cooler.
    I've had it in the shop and they tried a few things: replaced 6 battery cells, then, when it started doing what it is now, I was able to drive it back and they replaced the ECU and the compromised battery wiring harness assembly. I was able to drive it back, like I said, because the issue going into drive/reverse is intermittent. Occasionally no lights come on, sometimes just the triangle, but lately all day today it's been the whole gamut, triangle, all warning lights, no ability to drive or reverse.
    Car ran and drive fine for a few days then hit the issue that it's been having after its latest stint in the shop. I've only dropped 500 into it so far plus a tow so I'm not too hurt about it but I really like the car and would love to get it running again. Reluctant to send it back to the shop as I doubt they'll find the issue since it's intermittent.

    From what I've gathered p3102 could be a few things, one of which is the AC? I'm using an OBDII and Dr. Prius to check the battery so to my untrained eye all the green bars going up and down look good when i'm on the battery health screen. Is it possible the battery itself should be in a working state but some heat sensor is causing an issue? The 12v battery comes up a lot too, how do I check that? The shop didn't mention looking at it which surprised me. Anyways, let me know. Thanks!
     
    #1 dogChair, Jul 3, 2026 at 4:03 PM
  2. dogChair

    dogChair New Member

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    couple more things: just went out again and managed to start it. The triangle was gone for a minute then came back. No warning lights other than that. OBDII didn't show any trouble codes at all...that's weird. Only things that were different were: there was a cloud covering the car for a bit and I started the car with the OBDII plugged in. Could that possibly affect the car?
     
    #2 dogChair, Jul 3, 2026 at 4:28 PM
  3. bisco

    bisco cookie crumbler

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    you can get a free load test for the 12v at most auto parts stores, or buy one and diy.
    leaving the old connected can sometimes cause strange behavior.
    you might need a better code reader, search for the autel ap 200:autel-maxi-ap200-go-buy-this.232861
     
    #3 bisco, Jul 4, 2026 at 2:35 PM
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  4. dogChair

    dogChair New Member

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    I'll drive the car (when it chooses to be driveable) to the auto part store down the street and ask for a battery test in that case. As for the reader I'm using a Panlong, one recommended off the Dr. Prius website. I'll look into the Autel though, if it can pinpoint prius codes more specifically I'd be interested. Or is that something only done by certain apps?
     
    #4 dogChair, Jul 4, 2026 at 3:08 PM
  5. ChapmanF

    ChapmanF Senior Member

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    Does that mean Dr. Prius is the app you're using with it? Last I knew, Dr. Prius wasn't a complete solution for reading trouble codes from the car.
     
    #5 ChapmanF, Jul 4, 2026 at 5:17 PM
  6. dogChair

    dogChair New Member

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    Yea that's what I'm using. I also tried the free version of torque but it was riddled with ads: I'm open to suggestions
     
    #6 dogChair, Jul 4, 2026 at 7:34 PM
  7. Brian1954

    Brian1954 Senior Member

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    See the link in post #3.
     
    #7 Brian1954, Jul 5, 2026 at 9:06 AM
  8. dogChair

    dogChair New Member

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    Alrighty got the battery checked. I see now people are recommending I buy the autel maxi and I'll see about that, does it have a paired app or something?
    From the pictures the 12v battery sits around 11.7 with the engine off and 13.7 on. The charging also seems bad/low.
    What's the recommended approach from here? Replace the battery or test the alternator somehow?
    Could the 12v battery being bad cause starting issues in the heat? Car fired right up when it was cool out, like usual.
     

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    #8 dogChair, Jul 6, 2026 at 8:13 PM
  9. pasadena_commut

    pasadena_commut Senior Member

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    I have Torque Pro and there are not any ads. It cost $5 (then, who knows how much now) which is close enough to "free" for me.
     
    #9 pasadena_commut, Jul 6, 2026 at 8:59 PM
  10. pasadena_commut

    pasadena_commut Senior Member

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    There is no alternator, there is only the inverter.

    11.7 is low, but not so low that the car should not start - IF it stays at that voltage. Do you have a multimeter or voltmeter? Even a cheap one from Harbor Freight? Measure the DC voltage at the jump point while somebody else tries to start the car. If the voltage drops to 10V or less then maybe the 12V battery is the problem. Digital meters aren't great for this test though, they often can't respond quickly enough. An old fashioned analog voltmeter is better, as the needle can move very quickly. Once the car starts the voltage should jump up into the 13 - 14V range. 14.5V is I think the maximum inverter output and I can't recall at the moment what the minimum is, but it is roughly13.5V or something like that.

    One way to rule out the 12V is to detach it (take off the ground) in the trunk, then start the car with jumper cables at the jump point from a known good battery. It doesn't need to be AGM for this test. It does need to be attached with the proper polarity though or bad things will happen! Since the 12V was detached all the codes should have been cleared, and any you see will have cropped up since the good battery was attached.
     
    #10 pasadena_commut, Jul 6, 2026 at 9:10 PM
  11. dogChair

    dogChair New Member

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    The car always starts, it just refuses to shift into drive or reverse when whatever the real problem is is happening
     
    #11 dogChair, Jul 6, 2026 at 10:09 PM
  12. pasadena_commut

    pasadena_commut Senior Member

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    That battery is at a very low state of charge. That may or may not have anything to do with your current problem, but it isn't good. See if you can borrow a battery charger with an AGM setting and charge it up fully. (Slowly, I wouldn't go over 4A, and 2A would probably be a safer upper limit on an iffy battery.) Testing an AGM battery isn't something that the little electronic testers do well. They are good at measuring CCA, but useless at measuring Ah. On this car, Ah is the thing that matters. Well, that and internal resistance. They may be able to determine that a battery is bad (because of very high internal resistance or very low voltage), they can't really tell you that it is good, because they will usually give a passing score to a battery with almost no capacity. To measure capacity accurately requires a long discharge test (at least hours) at a low current using a device like a DTL-150. For the purposes of working through the immediate problem hooking up a good 12V with jumpers with the internal battery disconnected will tell you definitively whether it is a weak battery problem or not. If it is, replace the battery and you should be good.

    Otherwise, you will need to check voltages at various places from the jump point all the way to the transmission control module. To start with I would verify that none of the fuses are blown.
     
    #12 pasadena_commut, Jul 7, 2026 at 1:47 PM
  13. bisco

    bisco cookie crumbler

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    if the car is making 'ready', it's not the battery
     
    #13 bisco, Jul 7, 2026 at 2:08 PM
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  14. bisco

    bisco cookie crumbler

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    it could be corrosion on the ecu pins and/or plug, or anywhere between there and the 12v source
     
    #14 bisco, Jul 7, 2026 at 2:09 PM
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