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Discussion Starter · #1 ·
So I know the Mazda 3s are pretty notorious for having transmission problems and shifting into safe mode (3rd gear), but I think I've found an edge case here. It's a bit of a story, so here goes...

tldr; Mazda 3 rapidly hard-shifts to 3rd & back & throws U0101. Like 10 times a second. Anybody else seen this?

I have an '06 Mazda 3 5-door, 5spd automatic, 90k miles.

About 6 months ago the speed sensor went out on the transmission, resulting in hard shifts into third gear. It would come and go, and after I replaced the speed sensor on top of the transmission it went away and everything was great.

Fast forward 6 months. After a 450 mile drive from CO to UT, a similar problem arose, but throwing a different code—U0101. What would happen is the lights that indicate what gear I was in (Drive, Neutral, etc) would turn off, the AT light would come on, and the transmission would be stuck in 3rd. After a few minutes of driving, it would turn off and everything would go back to normal. We took it to the dealer and they weren't able to diagnose it. They said it was most likely some type of electrical short. They said it wouldn't cause the transmission harm to drive, so we drove back to CO.

On the drive it hard-shifted to 3rd every 90 miles or so, AT Light would come on, then it shifted back to 5th 5-10 seconds later and the light would go off. It was pretty much like clockwork. We got home OK, but then within a few days of very very light use something new started happening.

The transmission would go into "safe" mode and back very very quickly. 6-10 times a second, which made it totally undriveable. So we had it towed to the dealership and after a week or so they said I had to replace the engine wiring harness... Didn't make sense to me, but I was happy with some type of diagnosis. Then when I was calling back to get the part and OK the work to be done, they told me a needed a new transmission. I'm guessing they were trying to get money out of me. So i had the car towed home, where I was able to drive it into my garage without any problems.

Anyways, after researching this problem for a while, I think I'm going to get a new TCM, since that seems to go bad a lot, and technically that's what the engine code is calling for. Just wanted to see if anybody else has had this same problem and what they died. Otherwise I'm here to document how to fix the problem so others can solve it.

Let me know what you've done to fix this problem if you've seen it. Thanks.
 

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Update: I ordered Mazda part #L32E-18-9E1D (TCM) and had it installed in half an hour or so. The car has been driven 60+ miles without any sign of the problem.

I'll add this: The Mazda dealership told me the tested the TCM and that it was good. Don't believe them—if you're having these symptoms, I'd suggest you replace the TCM before anything else.
 

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Wow Bravo to you sir! Dont listen to anything the Stealership says. Always get a second opinion. And you at least used the code that was tripped to aid you in the repair. That right there shows that those engine codes are there for a reason.
 

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Just had U0101 last night.

2007 5 AT at 175k miles

It had slight hick up once right before getting out of freeway, got home safely, smooth.

2 hours later, start car and shift select to D range.
Immediately limp mode.

U0101 stored.



Replace L34T189E1E ( I paid like $487)



Module is under battery case. 3 bolts holding in place.

Service manual said, be careful not to damage silicon resin filled surface( back of TCM module)

connect back and luckily it was simple repair. 20 min to complete.



Glad I didn't pay at dealer for diagnosis and retail parts price of $650 + whatever labor they may charge.
 

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A week ago my 2006 mazda 3 GT jerked while driving and I noticed AT come on. It happened for just a second. Then in about an hour same. Once the light came on while sitting on red light. It stays for a second or two.

I was low on ATF, and overdue on its drain and refill. So today I went ahead and drained and even replace the filter. Refilled it. I only bought 4 qts, and I am still low on ATF. I am going to add another qt. But I still decided to drive it. I drove it for about 20 minutes and on while sitting on red light I saw AT come on for a second or two. So I drove back home.

Am I looking at the same problem as described above? I haven't pulled codes yet though. Will do that tomorrow.
 

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Mine shifts down to 4th and stays in 4th until the at light goes off then it shifts back to 5th. It is very random when it does it and I changed both speed sensors already because it was throwing the p0720 code. After changing the sensors twice there has been no change and still the same code. Do you think mine could be the same outcome of the tcm? It will shift into the lower gears as I slow down but WILL NOT go into 5th as long as the AT light is on. Sometimes I can stop and put the cat in park and then in drive and it will be fine for a while, other times it will go 1-200 miles before it comes back on.
 

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Update: I ordered Mazda part #L32E-18-9E1D (TCM) and had it installed in half an hour or so. The car has been driven 60+ miles without any sign of the problem.

I'll add this: The Mazda dealership told me the tested the TCM and that it was good. Don't believe them—if you're having these symptoms, I'd suggest you replace the TCM before anything else.
OMG this is 90% identical to the issue I am currently having except my car goes from 5th to 4th and it doesn't do it on every drive but my commute is long and I need my car to be reliable.

I have went to the shop twice. The 1st time they said that they did not see any codes and were not able to replicate the symptoms so they could not recommend doing any work (I can respect that (but I know something is wrong). They could only replaced the fluid and transmission filter. Although it did not happen for a couple weeks afterwards, about a month after the fluid change, it continued to happen and even got worse. My car is currently at another shop and after the diagnosis, they said they could not replicate the symptoms and there are no codes (same as the first place).

I know you did a 60 mile update. How was it after that? This post gives me hope!! Hope to hear from you soon!
 

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So I know the Mazda 3s are pretty notorious for having transmission problems and shifting into safe mode (3rd gear), but I think I've found an edge case here. It's a bit of a story, so here goes...

tldr; Mazda 3 rapidly hard-shifts to 3rd & back & throws U0101. Like 10 times a second. Anybody else seen this?

I have an '06 Mazda 3 5-door, 5spd automatic, 90k miles.

About 6 months ago the speed sensor went out on the transmission, resulting in hard shifts into third gear. It would come and go, and after I replaced the speed sensor on top of the transmission it went away and everything was great.

Fast forward 6 months. After a 450 mile drive from CO to UT, a similar problem arose, but throwing a different code—U0101. What would happen is the lights that indicate what gear I was in (Drive, Neutral, etc) would turn off, the AT light would come on, and the transmission would be stuck in 3rd. After a few minutes of driving, it would turn off and everything would go back to normal. We took it to the dealer and they weren't able to diagnose it. They said it was most likely some type of electrical short. They said it wouldn't cause the transmission harm to drive, so we drove back to CO.

On the drive it hard-shifted to 3rd every 90 miles or so, AT Light would come on, then it shifted back to 5th 5-10 seconds later and the light would go off. It was pretty much like clockwork. We got home OK, but then within a few days of very very light use something new started happening.

The transmission would go into "safe" mode and back very very quickly. 6-10 times a second, which made it totally undriveable. So we had it towed to the dealership and after a week or so they said I had to replace the engine wiring harness... Didn't make sense to me, but I was happy with some type of diagnosis. Then when I was calling back to get the part and OK the work to be done, they told me a needed a new transmission. I'm guessing they were trying to get money out of me. So i had the car towed home, where I was able to drive it into my garage without any problems.

Anyways, after researching this problem for a while, I think I'm going to get a new TCM, since that seems to go bad a lot, and technically that's what the engine code is calling for. Just wanted to see if anybody else has had this same problem and what they died. Otherwise I'm here to document how to fix the problem so others can solve it.

Let me know what you've done to fix this problem if you've seen it. Thanks.
[


we had a 08 Mazda3 with 227000 miles that issue started. I assumed the transmission was btr... transmission shop that was crooked charged me $3,200 for rebuilt transmission. 6 months later it's acting up, I called the transmission shop he finds a used t c m installs it and plays hero! Fast forward 2 years and 25000 more miles does the same damn thing ....I do research,,, order a new $550 t c m installed it in 25 minutes as recommended it to hang it off the brake lines, haven't had an issue since!
 
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