p0126 persists after new parts and various attempts

Discussion in 'Mazdaspeed 3 Troubleshooting' started by MortalMechanica, Dec 27, 2019.

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  1. MortalMechanica

    MortalMechanica Greenie Member

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    Solved the bubble issue. Turns out there was a pinhole tear in the upper hose.

    However, the problem persists despite being vacuum bled. I showed the video to a local friend and we tone tested the engine harness from the ECT to the PCM again. I found no issues and the ECT is reporting the correct resistance.

    Leaving me with 2 final options.

    Intermittent fault of the Harness
    PCM failure.

    given that a temp swing of 200 to 160 would cause some kind of metallurgical issue, or at least would damage the water pump I feel... AND having probed the harness and finding it in good condition with no tears and no amount of shaking or wiggling or vibrating the wires seems to have any effect... I'm gonna see if I can get a PCM on it.

    Will update if I find a fix. I spoke to someone recently who had the exact same issue and went as far as replacing the head gasket which didn't solve his problem. Unfortunately, he traded the car in before it was solved. He just left it alone until he got rid of the car.
     
  2. Enki

    Enki Motorhead Platinum Member

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    Hit the block with a temp gun before you go all that far in.
     
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  3. MortalMechanica

    MortalMechanica Greenie Member

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    Used a FLIR Camera to confirm that the temp was normal in initial tests and that the Thermostat was opening and closing properly. This led to the first couple of ECT sensors that were used, they were also tested as well as the harness was tested.

    It's possible that because of the intermittent nature of this fault that it could be the engine harness still. But none of the tests confirm that the harness is bad. All of the electrical testing shows that everything should be good, however, it's also possible that it just hasn't been tested while it was showing a fault, and it's incredibly difficult to.

    It's possible that engine vibrations cause the harness to intermittently lose contact with the ECT sensor, but I feel that if that was the case, The data logs would have shown a MIN/MAX/OutofRange value that is common with shorts or broken wires. Not a drop in coolant temperature that recovers. I don't even think the two wire ECT's are capable of changing in reading that quickly.

    I'll test it again, but I'm essentially just repeating all of the tests at this point with no clear forward path.
     
  4. Sho

    Sho Gold Member

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    Had similar issues, swapped t stats and ect sensors many times. Ended up pressurizing the system and found coolant slightly spraying out of the side of head near the water outlet neck.

    Ended up being HG failure along with stretched headbolts/lifted head
    20180613_200232-01-01.jpeg
    20180613_200252-01-01.jpeg IMG_20180613_162933-01-02.jpeg

    Usually if its just the t stat stuck open, you'll trip the p0126 code as soon as temp drops below 160*. But the car wont over heat ever. It'll just wildly swing between 150 and 190 or never warm up past ~160 once the coolant temp drops when it sticks open
     
    Last edited: Feb 14, 2020
    Sho, via a mobile device, Feb 14, 2020
    #24
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