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Help! Prius throwing C1241 and C1300 codes despite new HV and 12V batteries

Discussion in 'Gen 2 Prius Main Forum' started by sworzeh, Mar 26, 2024.

  1. sworzeh

    sworzeh New Member

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    Hey all,

    I just installed a new hybrid battery (brand new OEM) a couple weeks ago after the fire from my previous thread. Everything seemed to be going fine, then I got the red triangle of death with VSC and ABS lights so I pulled over. It initially said, "There is a problem with the transmission P lock mechanism. Park your car on a flat surface and fully apply the parking brake." Then it never said that again. Ran the codes on Dr. Prius and got P3102 and P3108. Then I ran Techstream and got only C1241 and C1300. The car still drives. The Dr. Prius codes haven't come back.

    My 12V was reading low, in the 11s, and it was 4 years old so I replaced that. The C1241 and C1300 codes remain. I can't find any successful solutions to these nonspecific codes on this forum, as most suggest to replace the 12V which I just did today with an OEM brand new battery that reads >12.4V.

    The car is also acting funny, the dash dimmer lights no longer work and they stay at a constant brightness, they also don't dim when my headlights are on. When I pull up the Prius' diagnostic codes, "ADIM/TCAN" swaps between DIM and bright repeatedly. When I go into accessory mode there are no dash lights in the car, but the main screen comes on. It's very strange.

    Has anyone successfully fixed something like this? Could it be the engine ECU? I don't want to break off all the vents again removing them to get into the dash (they're extremely brittle from being in the sun all their life) for something that may not work.
     
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  2. sworzeh

    sworzeh New Member

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  3. bisco

    bisco cookie crumbler

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    c1241-faut-code-abs.208054

    see post #6, but make sure your new battery is close to 13 volts after having been off for a few hours.
     
  4. Tombukt2

    Tombukt2 Senior Member

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    At ready. What's voltage reading on 12V??
     
  5. dolj

    dolj Senior Member

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    Something to consider is that C1241 is about the voltage arriving a the B+ at the VSC ECU.

    There are 4 sub-codes for this DTC and knowing which one might help pinpoint the area at fault. The sub-codes are 81, 82, 83, and 84.

    The repair manual has this to say:

    This code and C1242 are memorized when the power source voltage for the skid control ECU drops or the voltage for the ABS NO. 1, or ABS NO. 2 relay operation drops.

    Codes may be memorized when the voltage of the auxiliary battery temporarily drops.

    When the power source voltage is too high, the skid control ECU stops functioning and outputs no DTCs, and the ABS and BRAKE warning lights remain on.

    HINT:
    DTC C1256/56 (accumulator low voltage malfunction) may be memorized if the power source voltage drops.


    The full workup can be found here.
     
  6. sworzeh

    sworzeh New Member

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    The new 12V reads 12.75V on my multimeter brand new from the dealer with the car never ran.

    The previous 4 year old 12V reads 12.38V after it sat for 3 days. That one is no longer in the car.
     
  7. sworzeh

    sworzeh New Member

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    Thank you. My sub-code is 81 according to Techstream.

    I found that guide on here previously and I've went through #1 (no HV codes), #2 (brand new 12V installed and reading 12.75V before ever being used with date of manufacture last month), and #3 (plugged in my wife's working brake control power supply tonight with no change in the codes).

    #4 and #5 are somewhat confusing to me, as I don't understand how to check the voltages for each individual wires. I can't find any videos of this either. My multimeters metal prongs are way too large to fit in between those tiny wires. Any tips for checking this? I was debating on just replacing the skid control ECU with a working used one because I have no idea how to check this.
     
  8. sworzeh

    sworzeh New Member

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    Noted. I compared my Prius' lights with my wife's gen 2 and actually my lights are working properly. The dimmer only turns on when the headlights are on and the MFD doesn't come on in accessory mode in either car, and hers has no codes and works perfectly.

    So I'd like to redact that part of my entry paragraph and note that I think the brand new 12V is completely fine. It read 12.75V without driving the car.
     
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  9. dolj

    dolj Senior Member

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    To get that sub-code these conditions need to be met:

    System 1 is under the following conditions when READY is on:
    • Linear solenoid cannot receive enough current (brake is applied).
    • BS voltage is less than 8.9 V for at least 3 sec. (brake is not applied).
    • 12 V–power source voltage inside ECU is less than 8.5 V when the main relay is opened or VCM voltage is less than 4.7 V or 5 V or more for at least 0.05 sec.
    Trouble areas are:
    • ABS No.1 relay
    • Harness and connector
    • Skid control power supply circuit
    • Brake control power supply assembly
    • Hybrid control system
    The troubleshooting tree should take you through steps to test each item and find where the problem is. For some of the items you just need to apply common sense and best practice. Like when it says Harness and connector, you check the harness and connector for good connection and wires for damage and breaks.
    You need a set of back-probe wires to use in conjunction with your DMM. They have very fine (and sharp) probes so you can slip them into the back of a connector wire so you can check them in place.
    This sounds like an assumption. It's new so it has to be good, right? If you haven't actually checked the voltage, you should do that.

    You need to actually check #3 when you get your back-probe wires Otherwise it is just more assumption and no knowledge.

    Use your new back-probe wires to do #4 and #5.
     
  10. sworzeh

    sworzeh New Member

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    I've ruled out:
    • Brake control power supply assembly (tested with my wife's working one that isn't throwing any codes, I will also use the back probe on this when I get it but I'm not hopeful as I put a known working one in there with no success)
    • Hybrid control system (no HV codes and a brand new OEM hybrid battery, the decision tree says to skip if "DTC is not output")
    • 12V

    Still on the differential:
    • ABS No.1 relay
    • Harness and connector
    • Brake control power supply assembly

    My next goal is to take apart the dash to get to the wire harness and connector. I believe that's on the driver's side and I have to take off a couple air vents to get to them. Might have to wait until this weekend as I work above full time as a surgery resident.

    Yep the 12V was just tested by me at 12.75V. I can drive it first and check it again if you think that would be beneficial. This was undriven, straight from the dealer.

    Perfect thank you! Couldn't find that info online with what I was searching. I'll buy that at Harbor Freight. Because I am probe illiterate, I just put the red probe into the wires I'm testing and the black probe on something metal in the car, correct?
     
  11. mr_guy_mann

    mr_guy_mann Senior Member

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    As long as the chunk of metal is actually a good connection to (chassis) ground.

    Posted via the PriusChat mobile app.
     
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  12. dolj

    dolj Senior Member

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    You need to check it now after it has been installed in the car.

    Incidentally, did you clear all codes after you installed the new battery, just be sure you're starting with a clean slate after a possible fix? If not, do that then drive the car. You will need to restart the diagnostic from the beginning if the codes come back.
     
    #12 dolj, Mar 27, 2024
    Last edited: Mar 28, 2024
  13. sworzeh

    sworzeh New Member

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    Big Update!

    I went to the junkyard and got a skid control ECU out of a wrecked but overall very beautiful condition 2007 Prius for super cheap, like $25. I didn't want to pop off the dash to try it in my car, so I snuck my hand in above the driver's side gas pedal and unhooked the 4 connections into my skid control ECU and into the "new" junkyard one. It was quite hard to get these unhooked but thankfully my hands are tiny.

    Immediately codes C1241 and C1300 disappeared, but they were instead replaced with C1256 (Accumulator low pressure) and C1391 (Abnormal leak of ACC Press). I thought these codes may be due to my lack of calibration, so I pressed on with Techstream. I tried multiple online guides for this and none of them were detailed enough for my lack of knowledge, but then I found an amazing youtube video by one of our Priuschat members Jo that detailed exactly how to calibrate it step by step.

    The video is here:


    I reset the battery again and all the codes are gone now! I'll need to officially install this because I was too afraid to take off the dash but this is the first time I've ever not seen these codes at startup immediately after reset. There are no videos of how to install a skid control ECU so I'll try to make one.
     
    #13 sworzeh, Mar 28, 2024
    Last edited: Mar 28, 2024
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  14. sworzeh

    sworzeh New Member

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  15. dolj

    dolj Senior Member

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    Can you edit your post? Those codes should be C1241 and C1300.
     
  16. sworzeh

    sworzeh New Member

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    Fixed! Thanks for the heads up. Hopefully this post can help someone else with these codes.
     
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  17. TheLastMojojomo

    TheLastMojojomo Active Member

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    Glad I could be of help @sworzeh! (y)
     
  18. Longinus876

    Longinus876 Junior Member

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    I've got all sorts of crazy things going on too. Last scan showed 9 codes. Something strange is going on here. I suspect water intrusion, which is common for the 12v battery area. But the front cowl on the passengers side is also a problem. There are what look like modules located behind the glove box, in the area of the cabin filter that's directly under that area. My car had damp carpet on that side for a while and it was caused by that cowl getting plugged and water not draining. I think inspecting the connections (plugs) might be a good idea. Unfortunately all the wiring is packed in like sardines.
    Bottom line; Known problems with gen 2 Prius include water intrusion. Check all the connections.
    And why is nobody using dielectric grease??? The only place I see it is on the headlight plugs.
     
    #18 Longinus876, Jun 22, 2024
    Last edited by a moderator: Jun 23, 2024
  19. Tombukt2

    Tombukt2 Senior Member

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    I use it a plenty there's also sprays and other sundry wire drying concoctions generally I make sure water's not getting in my car I like to do that even more so I'm not driving around a will and Ted terrarium so there's always that It's easier for me to make sure that water's not ingressing then it is for me to try and take computers apart glove boxes out half the dash loose to unplug wires to blow them out and to spray them off and to plug them up and have them work again oh that is annoying yeah I generally try to find any of the leaks and get that sorted upon getting the car and then keeping it out from under trees keeping the well around the rear hatch clear no black funk and mold and tree stuff growing in it none of that I've been addresses and seen plant matter growing out of the hatch well lifted up and there's green moss and plant material growing out of the dirt that's an inch thick level with the gasket I mean this is how people keep their stuff this is not a rare one of incident either I go to these cars that people's address and get to see how they live pretty regularly