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Thread: AT light on, but no codes, and over revving

  1. #1
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    AT light on, but no codes, and over revving

    Hi all, I have a 2010 Mazda5 automatic with about 90k miles.
    Recently the AT light has come on and stayed on, even after restarting the car, and there are no codes.
    Only way to reset the light is disconnecting the battery. A few days to a week later, the light comes on again and no codes, even trying multiple scanners.
    Its done this about 3 times in the last few weeks and just happened again.
    I'm not the regular driver of this car (my wife and daughter are), so I've never had the light come on under my control.
    They say the car drives and shift fine, but sometimes feels like it over revs a bit sometimes, or at least they think it does.
    Tonight when it did, and the same... AT but no codes. I cleared the AT light (disconnecting the battery) and went out driving it easy and it was fine.
    Towards the end of the driver I started laying into I and got it to over rev, meaning it felt like it should or was about to shift, but continued to rev with no additional torque to the wheels. I got it to do this 2 or 3 times before pulling in the driveway.

    So, it means the others are driving the car harder, and this over revving is likely eventually turning on the AT light.

    Has anybody experienced this? Thoughts? AT light with no codes or none detectable scanners. Pushed hard and over revs.

    Rather hear what you have to say before going to the dealer or trans shop, pay for diagnosis and hear suggestions of what to try for $x dollars to hopefully address it.

    PS, I tried the 3x trans drain and refill last week using Castrol Transmax Import.

    Thanks

  2. #2
    Registered Member MZ5black's Avatar

    2014 Mazda5 Sport Auto

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    Aug 2015
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    West MI USA
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    Strange... A/T light on and no codes. That surprises me.

    Did you attempt to read codes using an OBDII code reader like those sold at auto parts stores and/or have a store employee do it? I'm wondering... do Mazda A/T codes require a special tool to be read, i.e. a more expensive and sophisticated one than the commonly used OBDII scanners? I have a couple of scanners -- both relatively inexpensive -- and while they've helped me on a number of occasions with engine-related issues in various cars, I can't remember ever getting any codes for A/T and I don't think I've had the ECU read in my 5 period... so thought I'd check. Hopefully others can offer an opinion or share their experiences. But if you're in the US/Canada, your closest dealer will certainly have the needed tool.

  3. #3
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    Yes, I tried retrieving codes using a couple different brands of readers, that I've used successfully on any/every other engine related check engine lights I or anybody I know have used either for. So the questions are... is it possible to have the AT light and no code, or am I stuck going to Mazda? I don't want to go to Mazda to pay $100 and be told there are no codes, and then have them start guessing at what to get me to try at my expense.

  4. #4
    2008.5 MGM MS3 rsvinylgraphics's Avatar
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    Do you have an AAMCO near you? they read trouble codes for free and I am sure they would be able to read the Mazda codes with their equipment....

    https://www.aamco.com/

  5. #5
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    I've never heard of them. Was thinking they must be a US chain, but they are in Canada too. Unfortunately none within an hour of me, but something to consider. Thanks

  6. #6
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    I went to a local garage and they retrieved a P0744.
    Torque convertor clutch pressure control solenoid intermittent.
    Finally have a direction to go!

  7. #7
    2008.5 MGM MS3 rsvinylgraphics's Avatar
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    P0774 Potential causes:

    -Wiring harness to transmission damaged, loose connection, or intermittent open/short circuit
    -Torque converter clutch (TCC) solenoid
    -Transmission control module (TCM)

  8. #8
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    Thanks. Where are those causes from, and are they the only 3 possible or just 3 of "x" possible codes?
    Not challenging, just curious and anxious to learn.
    How should I proceed?
    1 sounds somewhat straight forward
    2 and 3, are there tests?

    Thanks

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