What's wrong with my 2006 Mazda3... transmission Problem?

Guys I just got Check engine light ON and when I change gears I only see AT light up. The car drives but jerks hard when shifting into gears R and D. Does anybody know what could be wrong?

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3I or 3S (2.0L or 2.3L)???
How many miles??
What are the codes for the CEL???

But it sounds like you need a transmission shop to check it out for you…

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You have a gear shift indicator in the instrument cluster and it is NOT lighting up to indicate what to indicate P, R, N, D, etc . . . ?!

Please confirm your scanner does NOT communicate with the automatic transmission control module

Then check the appropriate fuses. Most likely, none have blown

If that is in fact the case, it’s very likely the automatic transmission control module has failed, in which case you need to replace with new or have it rebuilt

If you’re able to do everything I just suggested yourself, you should be able to get out of this with just the cost of a rebuild . . . $250 - $300 range . . . if not, you’re at the mercy of others, who may misdiagnose or sell you something more expensive which will either not fix the problem or drain your wallet unnecessarily


Hi guys, I did a basic scan on the car with my obd app and this is what showed up.

I am guessing TCM is the problem but I also see some message about ECM. Do you guys think that ECM is the problem too? I called around but nobody fixes it locally. Dealer wants $1100 for it. I am Canada and I found one place in Ontario called Xemodex.ca that fixes it when I send the unit to them for about $360 + shipping. I also found company called Flagship One that just sends you a “new” or remanufactured (I don’t know) unit for $500 Canadian. Does anyone know anything about these companies? Or know any other that do this kind of work? Is it better to get the original unit fixed or get one from Flagship one? What about the ECM message am I getting it only because the TCM is not communicating with it and ECM is good? Thanks

I have 2006 Mazda 3 2.3L with 210,000 km on it.

the most common cause of U0101 is a wiring issue. Specifically with the CAN bus system. Here’s how to go about tracking down an issue with the wiring to/from your TCM.

Check the TCM fuse(s) and make sure that it is not blown. Make sure your 3’s TCM has power. This does happen and is very easy to check.
Check all grounds going to the TCM and verify that they are secure to the chassis/frame. You’ll need to clean them up if they have been corroded.
Trace the power and ground wiring and see if they have been damaged in any way. Check it for open/shorts. Repair the wiring harness as needed.
Inspect the harness connections. Once you’ve established that the wiring harness looks fine, the next place to look is where the wiring harness plugs into the TCM and CAN bus. First, unplug the harness from the control module. Once unplugged, inspect the pins to see if there is any damage to them. If one or more of them look discolored compared to the rest of the harness, that is likely to be what’s causing U0101. You can use an electrical contact cleaner to clean the harness pins properly. If they look damaged beyond cleanable corrosion, you may have to re-pin them.

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The first priority is to address the U-diagnostic codes. You car will never work correctly unless all of the modules are able to chit-chat with each other. Suggest to start with a basic battery/charging system test, as the power supply voltage to all of the modules have to meet the minimum spec voltage, otherwise the modules aren’t able to communicate properly.

Esp of the jerking symptom when engaging R or D occurred prior to this most recent symptom, that could be a totally different issue. Maybe some of the engine or trans mounts need replacement.

Where is the TCM fuse located and how do I check it if its not see through?

Your TCM is bolted to the top of the transmission

You’ll have to remove the battery, tray and engine control module to access the TCM

Trust me, from a professional standpoint . . . in all likelihood, your TCM needs to be rebuilt

The good news is that it won’t be very expensive

A word of advice . . . do NOT buy a used TCM which has not been rebuilt. It’s very likely to fail in a short amount of time, just like yours

I have personally dealt with this company

Don’t buy a $1000 new module . . . that’s too expensive, imo

And btw . . . this TCM is plug-and-play. No programming required


A used Tcm could cost $40 at junkyard. And work fine. The future is hard to predict.

A colleague at work has the same Mazda 3

He said he went to several pick-a-part type of junkyards and ALL of the Mazda 3 tcms were already scavenged

That should tell us something . . .

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@Erikmarko72_186627 Any updates? :smiley:

I sent the TCM unit to Xemodex.ca it will cost me about $440 Canadian dollars including shipping to get it refurbished. I will let you guys know if it will solve the problem.


Did it look ok by visual inspection? Often PCB circuitry problems show up as brown areas (indicating overheating) or small cracks in the pcb metal traces, often in the brown areas . The latter often require a magnifying glass to see. Its possible though a single part could fail with no visible signs apparent.

Years ago we had a local car talk radio program hosted by Paul Brandt. One program he had taken his car to the local precision tune who was a sponsor. The owner had opened up the ecm and replaced a faulty component. Don’t remember if it was a transistor or what but was fixed for a few dollars. If you can get this stuff open,have the knowledge to test, and can get the part, no need to cost a lot.

High tech electronics technicians do this every day, just part of the job. They hardly ever replace the entire pcb, only the part that failed. Doing this job quickly typically requires training what to look for & probing the circuit w/an o’scope, not skills the typical car-repair diy’er has. But sometimes a diy’er can get lucky just by doing a visual.

You would have to cut away the “potting” to get a good look

The place I dealt with said they would absolutely refuse to work on an modules that have already been “messed with” . . . something to consider


I would agree with that. This is truly better left to folks that “mess with” this stuff every day.


Yes, the unit was sealed with some kind of rubber or something and there was no obvious sign of failure of the unit.

Please let us know when the repaired tcm is installed and your car’s fixed