2008 Prius C1241 and C1242 - Won’t start or go into ready

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Tigerpilot76, Apr 29, 2020.

  1. Tigerpilot76

    Tigerpilot76 New Member

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    I have a 2008 Prius that threw codes C1241 and C1242 and the skid control buzzer came on. Now it won’t start. It also has 12 volts to the jumper terminal but no power to the OBD port, the display isn’t lighting up, the door locks aren’t working with the button inside the car, but the headlights work, and the brake booster powers up.

    I bought this car used but like new and I’ve put the majority of the 380k miles on it. I drive it about 900-1000 miles a week back and forth to work. In January I put a new 12V battery in it. Immediately after installing the new 12V battery, the display didn’t work, and it had never had an issue before. I disconnected the battery and the display worked again. Now at least once a week I have to do this procedure again. So last week when I disconnected the 12V battery then tried to restart it, it wouldn’t boot up the entire system. After several tries it finally worked. So then I left for work and after 45 minutes of driving, several lights lit up and the skid control buzzer started going off. I just happened to have my code reader computer with me and checked them on the fly. It was C1241 and C1242. I made it to work but the next morning my Prius wouldn’t start. It has 12 volts to the jumper terminal on the front but the door locks don’t work and the OBD port doesn’t have power. I’ve checked all the fuses and tested the ABS 1 and 2 relays and both are good. My next step is to test the skid control plug for power. Does anybody else have any suggestions?
     
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  2. dolj

    dolj Senior Member

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    You may have a failed combination meter (CM). You can get a repaired one from Matt @Texas Hybrid Batteries (Prius Speedometer Replacement) in exchange for your old one, or send him your old to repair. If you are ok doing board level repairs you can replace the failed capacitor yourself. See the thread pinned to the top of this forum - Combination Meter Repair - DIY. The car might be starting, you just might not know because you are not seeing the dash light up the way you are used to. If you press the go pedal, the ICE should startup if it was indeed READY to drive.
    The only thing that springs to mind is loose connections at the battery. Check the +ve & -Ve battery terminals and where the ground (-ve) connects to the car body on the rear panel. They should be clean and tight.

    Another possibility is the Brake Control Power Supply (BCPS) assembly. This is a bank of large capacitors and if one or more of the capacitors has failed it can throw these codes. The BCPS is located right next to the 12 V battery, inboard. It also won't hurt to check the 12 V battery and charge up if necessary.

    Here is the troubleshooting diagnostic trees for these two codes.

    DTC | C1241/41 | Low Battery Positive Voltage or Abnormally High Battery Positive Voltage
    DTC | C1242/42 | Open in IG1 / IG2 Power Source Circuit


    PS. Don't be mislead by the one-liner test for C1241, it is talking about low (or high) voltage at one of the brake system ECUs.
     
    #2 dolj, Apr 30, 2020
    Last edited: Apr 30, 2020
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  3. bisco

    bisco cookie crumbler

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    a health battery would be 12.7 volts, you can live with a few tenths less, but not 12
     
  4. Tigerpilot76

    Tigerpilot76 New Member

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    The CM has been going out ever since I changed the 12V battery in January. I’ve driven plenty of miles with it off because I was in too much of a hurry to reset it. So I checked that first thing, it won’t switch out of park. And also the ICE doesn’t turn on, this time there’s a lot more to it than usual. I’m getting it out of our parking lot at work soon, and as soon as I do I’ll be able to work on it easier. So far I’ve checked loose connections, checked voltage at the battery and the fuse box under the hood, pulled all related fuses and ohmed them, and pulled the ABS 1 and 2 relays and checked resistance on those too. I’ll check the BCPS next since it’s easiest to get to and I already have everything out of that area so that I could check the battery. Then if that checks good I’ll move on to the skid control ECU.
     
  5. dolj

    dolj Senior Member

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    I wasn't suggesting that this (CM) was the cause of your issues, but merely one of two or more problems you have. Anecdotally, it does seem that something happens (sometimes) to the CM when a poorly performing 12 V battery is replaced with a new battery, but no explanation has been offered by anyone with electronics knowledge of why that is so, unless it is something to do with how the (failing/failed) capacitors react to the higher constant voltage from the new battery. The failed CM does set a code, so it would be an idea to fix this as it relatively cheap DIY ($150) vs dealer ($800-$1000 plus 2 weeks downtime). A light on the dash could mask other serious problems unless you scan regularly for new codes.

    Other than following the diagnostic tree linked to in my last post, I cannot offer anything else further towards resolving the other issue(s). You sound like you have a good handle on that anyway. Time and method should lead you to the point of failure.

    All the best.
     
  6. Tigerpilot76

    Tigerpilot76 New Member

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  7. Tigerpilot76

    Tigerpilot76 New Member

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    Thanks for your help! I feel pretty comfortable that I can do a repair on the CM myself with the assistance from people on here. I’ll definitely work on that soon, it’s very annoying when it goes blank. Tomorrow morning I might get a chance to work on the other issue. I’ll see how that goes after working night shift. I’ll post updates when I have some.
     
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