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2012 AT TC lights w/ hard bump, subsequent AT failure

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2012 Mazda5 GT
2012 Mazda5 GT auto about 40,000 miles. Could not find quite the same issue on the forum, so making a post. I think I'm on the right track, but would appreciate advice and notes on similar experiences. AT = automatic transmission; TC = traction control

First Incident: about 2 weeks ago on Thursday. Wife experienced a quick series of bumps/jerks from the car at about 25 mph during a hwy on-ramp pull, and the AT and TC warning lights flashed on/off for a short time during this. Wife thought she was just losing traction on the wet pavement of a misty morning. I found out about this incident after the 2nd Incident...

Second Incident: next day, quick bump/jerk from the car, accompanied by a brief AT warning light. This after a steep uphill highway pull, down the other side, and iirc, I just let off the gas to coast a bit at about 65-70 mph. While on a weekend road trip with the family. And then the wife goes "Oh yeah, I meant to tell you that something similar happened yesterday..." Now she tells me. Car was otherwise fine for the rest of the outbound trip, including a number of hills. I checked the trans fluid at our destination, and it looked like it needed a change.

Third and Major Incident: return trip got into bumper-to-bumper crawl on a very hot day. Car seemed fine until we started getting back to highway speeds, then the bump/jerk, AT and TC warning lights happened again. This time it did not go away, and the car seemed to be slipping out of gear and trying to find the lower gear, but in quite a violent manner. I got the car off the highway and into a parking lot, but the issue persisted regardless of speed. I let the car cool off for about 45 minutes, figuring the old trans fluid was cooked after the blistering heat and no air flow in slow traffic. I barely got it out of the parking spot before the light show, transmission was slipping and jerking again. Put it back in a parking spot, got the kids some slushees, and called AAA.

By the time the tow arrived, the car had nearly 2 more hours to cool, and of course the tow truck driver had no problems backing the car out of the parking stall and driving it onto the flatbed ramp. No issues unloading the car either. Car ran, shifted, and drove just fine when cool. I figured it had to be the 7-year-old, thoroughly cooked trans fluid, and planned a DIY flush ASAP.

A week later (car not driven during this time), I did the drain and flush (very helpful videos available online!), ran through 12 quarts doing three at a time until the fluid coming out was nice and red. No grit or metal bits in the old oil, though it was definitely cooked. Car seemed perfectly well behaved for the next few days, noticeably smoother shifts, until...

Fourth Incident: last Sunday, got that jerk/bump and AT light like it slipped out of and back into gear while doing an uphill pull at about 65-70 mph, then back to normal - no warning light drives fine. I drove it more sedately without incident, and the car has behaved itself all week.

I've read a lot about bad TCMs, solenoid trouble codes, and related items. Can someone tell me if the car retains a history of trouble codes, even if a warning light is not currently triggered? If so, I guess my next step is to have a local parts shop run a code check.

Also, has anyone else had a similar experience with a '12 or newer 5? If you have, care to share?

Many thanks for your time - tons of great info from great folks here.
 
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2009 Mazda 5 GT
Went through this with my 09 this summer. The TCM is intermittently failing doe to overheating. That hard jerk feeling is the car going into limp mode which is 3rd gear, regardless of speed.

Before coming to the conclusion on my car, I read countless forums of people having the same problem and every single one that reported a fix said they had to replace the TCM.

Don't know about how long the codes are stored for, plugging in a reader is cheap or free and won't hurt anything. If you have your own reader (if not, they're not expensive and you can use it for years) you can plug it in the next time it's acting up and confirm. U101 is the 'lost communication with TCM' code.

Let us know what you find out and good luck.
 
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2012 Mazda5 GT
Thanks alawat82. Here's my an update on my experience so far:

1. Issue has popped up a couple times again since original post. Allowing the car to cool seems to remedy the situation.

2. The car is not throwing any codes - at least not when the AT light is off. As the trouble light does not persist, we have been unable to get a reading while the light is on.

3. It seems that most incidents coincide with a hot engine... figure heat is messing up the TCM.

I am going to price out TCM units and likely DIY a replacement. If that does not work, then I'll be visiting a local transmission specialist. Will update as things progress.
 
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2012 Mazda5 GT
Update... I picked up an Innova 5110 CarScan Reader to see if I could initiate the same issue with the car, and catch the code live. Either the car had not thrown any codes yet, or the guy at the auto parts store did not know how to operate a reader to get to the ABS codes... After fiddling with the new reader in the parking lot, before even taking the car out on the road, I saw that the car is indicating the following codes, all ABS, as indicated by the scan tool:

1/5: U0248.64 - Invalid Data Received From Steering Angle Sensor Module
2/5: U0248.62 - Invalid Data Received From Steering Angle Sensor Module
3/5: U3003.16 - Battery Voltage
4/5: U3003.17 - Battery Voltage
5/5: U0101.00 - Lost Communication with TCM

I'm guessing these could be historical codes that have not been cleared, with U0101 being the latest. Is this correct? The car has not been experiencing any issues with battery/charging or steering/suspension. Perhaps they are all related to the TCM acting stupid when hot?

Can anyone tell me what the decimal codes mean? The two numbers following the standard code. The scanner display makes it look like a decimal with two digits after. See attached image that shows ".000" to the right of and smaller than the 5-characater code field.


I can't find this info through the regular online channels - maybe I am not searching the right terms. I have not tried to recreate the symptoms yet. Looking for more information before I do so.

Quick Update: chatting with Innova's support was useless. "Get our app!" was the only response. No reply regarding the additional three digits to the right of the standard 5 character code...
 
Last edited:
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2009 Mazda 5 GT
I just flipped through the manual PDF and you're right, it doesn't mention anything at all about the 3 digits after the code. It sounds like those are historical codes if you don't have a current CEL or ABS light, try clearing them and checking again in a day or two to see if they're still present.

U101 is definitely the 'your TCM is not working' code.
 
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2012 Mazda5 GT
Thanks alawat82. Yes, all the codes leading up to the U101 code were old. Battery voltage codes likely coincided with a recently replaced end-of-life battery. I cleared the old codes, and nothing has popped up in the last two weeks, including any TCM-related error codes. Weather has been cool, so the TCM has not gotten grumpy about heat.

Next step will be to examine the TCM and wiring... maybe cleaning the housing and connections will help. Gotta wait for a warm day to try and recreate the situation and catch a fresh error code.
 
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2012 Mazda5 GT
U0101 and U0100 are now regularly reoccurring. I picked up a refurbished TCM (L5E4 18 9E1E) from Module Repair Pro https://www.shop.modulerepairpro.com/. Got it within two days of the order being processed, so very good customer experience so far. The only thing I'm leery about is getting my full core charge back, including tax. Will cross that bridge when I come to it...

Brushing up on the R & R process now before making the swap later today. Will update... Wish me luck!
 
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2012 Mazda5 GT
Success! About two months since replacement, and the problems have not come back. Per my previous post, I did not get the tax charged at purchase for the core deposit fee back with my core deposit refund. I will have to take that issue up with the vendor. $13.50 is $13.50, especially when it's MY $13.50. Customer service experience was subpar - it was like trying to get answers out of a bored, resentful know-it-all. While I got my answers, it was not a pleasant experience.

The refurbished replacement part had a few extras to help combat the heat issue: spacers at the mounting points and a foam/fabric insulation patch on the bottom of the unit where it contacts the transmission housing. Mazda evidently had a service note suggesting zip tieing the replacement module to the brake lines on the fire wall in order to mitigate the heat issue - at least that's what I saw from one youtuber. The insulation and spacers on the refurbished TCM seem to address the issue, so no need to jerry-rig the TCM.

Not a difficult process - took about 30 minutes to get everything out of the way in the engine bay, 5 minutes to swap out the part, and 20 minutes to put it all back together. I did not need any special tools - just shallow and deep well metric sockets a socket wrench, and a few metric open-ended wrenches. Just don't forget to fully seat all the electrical connections (gave myself a scare when the car wouldn't start and ALL the warning lights were on because I did not seat and lock down the main connections), and replace all air lines (got a code for an O2 sensor line that I forgot to reconnect).

Good luck to you if you're undertaking this fix.
 
:
2009 Mazda 5 Sport
Success! About two months since replacement, and the problems have not come back. Per my previous post, I did not get the tax charged at purchase for the core deposit fee back with my core deposit refund. I will have to take that issue up with the vendor. $13.50 is $13.50, especially when it's MY $13.50. Customer service experience was subpar - it was like trying to get answers out of a bored, resentful know-it-all. While I got my answers, it was not a pleasant experience.

The refurbished replacement part had a few extras to help combat the heat issue: spacers at the mounting points and a foam/fabric insulation patch on the bottom of the unit where it contacts the transmission housing. Mazda evidently had a service note suggesting zip tieing the replacement module to the brake lines on the fire wall in order to mitigate the heat issue - at least that's what I saw from one youtuber. The insulation and spacers on the refurbished TCM seem to address the issue, so no need to jerry-rig the TCM.

Not a difficult process - took about 30 minutes to get everything out of the way in the engine bay, 5 minutes to swap out the part, and 20 minutes to put it all back together. I did not need any special tools - just shallow and deep well metric sockets a socket wrench, and a few metric open-ended wrenches. Just don't forget to fully seat all the electrical connections (gave myself a scare when the car wouldn't start and ALL the warning lights were on because I did not seat and lock down the main connections), and replace all air lines (got a code for an O2 sensor line that I forgot to reconnect).

Good luck to you if you're undertaking this fix.
As someone who also did this on their 09 this summer, the one thing that I thought made it easier were ratcheting wrenches. Not a big deal if you don't have them though.
 

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