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Thread: Transmission problems w/ 2008

  1. #1
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    Transmission problems w/ 2008

    Howdy,
    I have a problem with my m5 that I can't quite figure out. It comes in two stages:

    1. Started the car and put it into reverse. It shifted hard, then when I started driving, seemed like it was stuck in 3rd and the check engine and transaxel lights came on. I parked it and came back when I had time. The battery died by the time I came back to it (2 weeks, we don't drive it very often). I replaced the battery and the symptoms went away.

    2. Soon after this, at around 40 mph(usually, but also seen when turning into a parking lot) the car would start jerking like I got rear-ended a couple times and the check engine light would flash and then everything would be normal. I don't have any CEL bc I put the new battery in there and haven't really driven it enough to get codes(I assume)

    So, any suggestions?
    Ryan

  2. #2
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    2009 Mazda 5 GT

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    Sep 2017
    Location
    Indianapolis, IN
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    Have a similar problem with my 2009 that started last week. Went to back out of garage and felt a HARD shift going into Reverse. Check engine and AT lights immediately came in. Pulled a U101 code which means the transmission lost communication with the TCM (Transmission computer).

    Some research shows this is a very common problem. After so much time, vibration and heat the TCM will intermittently or completely fail and stick the car in limp mode which is 3rd gear. Rest of my trans is in excellent condition so I'm 95% sure it's the TCM.

    Sounds like yours is failing intermittently and the heat wave last week isn't helping the situation.

    Replacement TCM costs almost $700 at my local dealer but I found an ebay seller with a good reputation for fixing them for $200. The same seller offers an exchange where they trade an already repaired TCM with your non-working one for $300.

    TCM is bolted on top of transmission under the battery box, took me about 30 minutes to take it out. Expect to get the repaired module back early next week and I'll report back with the results.

    Hope this helps.

  3. #3
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    2009 Mazda 5 GT

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    Sep 2017
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    Indianapolis, IN
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    Forgot to mention, this is also common with 3's so if you are looking for videos on how to reach the TCM, there are a lot of people showing how to do it on mazda 3's. Replacement TCM also requires no programming but 3 and 5 TCM's are not interchangeable.

  4. #4
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    Yeah, I am also leaning towards the TCM. The common symptoms I find don't totally match up, however, so I am hoping others have had similar symptoms fixed by a repaired TCM to give me more confidence in the diagnosis.
    No longer being in limp mode bothers me. I wonder if that is because all the tests haven't been completed after replacing the battery.
    Thanks for the info, did you need any special tools to replace the TCM?

  5. #5
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    2009 Mazda 5 GT

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    Sep 2017
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    Indianapolis, IN
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    No special tools, hardest part was taking out the battery tray because of the tight fit. Have you hooked up a code reader? It should give you any recent codes so you can confirm if you're getting the U101.

  6. #6
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    I haven't hooked up a code reader, will it give me codes from before the battery died?

  7. #7
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    2009 Mazda 5 GT

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    Sep 2017
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    Indianapolis, IN
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    Depends on the reader, won't hurt to try and readers are inexpensive if you don't already have one.

  8. #8
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    2009 Mazda 5 GT

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    Sep 2017
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    Indianapolis, IN
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    Got my repaired TCM this week, works great and fixed my AT / CEL lights.

  9. #9
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    I bit the bullet and got the TCM repaired, works fine after 60 miles. Thanks for the info!

  10. #10
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    Alright, after about 100 miles of smooth driving, the dreaded CEL and A/T came up, the car started bucking, and U0101 came up. Back to square one. I am going to check all the connections and make sure everything is secure. Then, check the connector to the tcm. Anyone know what fuses to check?

  11. #11
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    2009 Mazda 5 GT

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    Sep 2017
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    Indianapolis, IN
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    Sorry to hear, where did you end up having the TCM repair work done?

  12. #12
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    Got it off of eBay, All Computer Resources.

  13. #13
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    2010 Mazda 5 Sport

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    May 2019
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    Contact them. Tell them it failed again. See what they say.

    They might have some troubleshooting tips.

  14. #14
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    Waiting on a reply from them. Since the car passed state inspection after the repair, I figure it is likely that it failed again, but I am working from a place of ignorance.

  15. #15
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    Got a reply:


    Please follow these steps to resolve your vehicle troubles:
    1. Disconnect Battery (30-45 Minutes)
    2. Remove Module and clean the plugs and pins thoroughly
    3. Clean and inspect the Module harness. Check for loose wires or bad connections
    4. Install module and be sure each connecter is fastened securely
    5. Reconnect battery
    6. Check that battery is fully charged
    7. Turn Ignition to 'ON' position for 3-5 minutes (do not start)
    8. Turn off ignition
    9. Start vehicle - allow multiple drive cycles for the new module to relearn your vehicle

    I'll try it out and report the results.

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