Can't replace 2016 Mazda6 TCM without replacing transmission?

[Lazy2.5]

OP, I would definitely look into having that done.

 

[LarryLondon]

Unsure if you've moved forward or not but I will also say that the tcm is indeed built into the valve body and the valve body is likely the issue. I have a 2016 Mazda 6 and the tcm is on the fritz. It will throw at, parking brake, engine, traction control lights randomly, go into limp mode randomly, and have the start button flash red and refuse to start occasionally. Every code, from engine light to the abs code is all tcm failure or lost communication with tcm. And it is an entire valve body and tcm assembly that needs replaced. I've reset the transmission, I've unhooked the battery, ECT. It'll drive fine for a week then freak out again. I even replaced abs sensors in case they were reading improperly and confusing the computer. My Mazda dealer says they've never replaced a valve body or tcm in these cars but can do it. Aamco says they can do it as well. The issue is it will need programmed to the vehicle it is installed in. They are vin locked. It can be replaced without replacing the entire transmission. I attached photos of the codes I have, if you don't have similar codes I don't think it'd be your tcm necessary. .

Thanks for that, good to know.

At this point I'm still driving the car and there has been no change to the behavior after 2 months.

I've still never had any codes, any transmission issues, any warning lights or any problems other than delayed engagement with a slight shudder when going from P to D on a cold engine. Other than that the car is still driving normally and the delayed engagement seems to be a minor isolated issue.

So I'm just continuing to monitor it and keep my options open. Replacing the valve body and TCM is over $2000 and I would probably pay that if I were sure it would fix the issue.

 

[Lazy2.5]

Valve body replacement will fix it.

 

[ceric]

OP,
If I were you...

1. I would drain-n-refill ATF a few times (2-3 times, you it once already) to clean up old fluid. I bet you never had it replaced before.. not the 1st owner either. So, it's over-due. Every drain-n-refill only gets to less than 1/2 of the fluid. Don't flush it.
2. I would reset the AT software by discounting (-) terminal for 30 mins and reconnect it. The entire transmission software will be reset and relearn your driving all over again.
3. if (1) and (2) do not fix it, I would trade it in to dealers of non-Mazda. Go there when your Mazda6 is fully warmed up. Let dealers deal with it. Yes, I won't feel good selling it to any private party. I have no problem selling it to dealers. They are professional.

 

[Silly Wabbit]

I'd highly recommend op to perform AT relearn which is on the first page of this thread. A simple battery disconnect will not relearn.

 

[sinistriel@]

OP,
If I were you...

1. I would drain-n-refill ATF a few times (2-3 times, you it once already) to clean up old fluid. I bet you never had it replaced before.. not the 1st owner either. So, it's over-due. Every drain-n-refill only gets to less than 1/2 of the fluid. Don't flush it.
2. I would reset the AT software by discounting (-) terminal for 30 mins and reconnect it. The entire transmission software will be reset and relearn your driving all over again.
3. if (1) and (2) do not fix it, I would trade it in to dealers of non-Mazda. Go there when your Mazda6 is fully warmed up. Let dealers deal with it. Yes, I won't feel good selling it to any private party. I have no problem selling it to dealers. They are professional.

Battery disconnect will not relearn the transmission behavior and learned values. Its written into the ROM of the TCM and needs to be told to begin again.

 

[LarryM]

Unsure if you've moved forward or not but I will also say that the tcm is indeed built into the valve body and the valve body is likely the issue. I have a 2016 Mazda 6 and the tcm is on the fritz. It will throw at, parking brake, engine, traction control lights randomly, go into limp mode randomly, and have the start button flash red and refuse to start occasionally. Every code, from engine light to the abs code is all tcm failure or lost communication with tcm. And it is an entire valve body and tcm assembly that needs replaced. I've reset the transmission, I've unhooked the battery, ECT. It'll drive fine for a week then freak out again. I even replaced abs sensors in case they were reading improperly and confusing the computer. My Mazda dealer says they've never replaced a valve body or tcm in these cars but can do it. Aamco says they can do it as well. The issue is it will need programmed to the vehicle it is installed in. They are vin locked. It can be replaced without replacing the entire transmission. I attached photos of the codes I have, if you don't have similar codes I don't think it'd be your tcm necessary. .

Hey Chris. I know this was from quite a while ago but just curious if you got this solved? I've had the same issue. I found a used tranny with 50k on it for $350, pulled TCM/Valve body and swapped it myself. $180 to program, although the car started and drove prior, so not convinced that it was actually VIN locked. Seemed to have worked, but then a month later (but 5k mi, I drive a LOT for work) it started glitching again What was maintenance history like on yours in terms of fluid and filter changes? Also, does your gear indication on the dash disappear sometimes when this happens? I found out the hard way that if that happens and you turn the car off it won't re-start

 

[ChrisMazdaG]

Hey Chris. I know this was from quite a while ago but just curious if you got this solved? I've had the same issue. I found a used tranny with 50k on it for $350, pulled TCM/Valve body and swapped it myself. $180 to program, although the car started and drove prior, so not convinced that it was actually VIN locked. Seemed to have worked, but then a month later (but 5k mi, I drive a LOT for work) it started glitching again What was maintenance history like on yours in terms of fluid and filter changes? Also, does your gear indication on the dash disappear sometimes when this happens? I found out the hard way that if that happens and you turn the car off it won't re-start

Yes, gear indication light will disappear, limp mode, engine lights, ECT. You can get a thick wire, you'll need two people, you can jump your starter with the battery and wire (subwoofer size wire) but you need someone inside to push the start button when you do it at the same time, and it will start again. If the car doesn't know what gear it's in (TCM acting up) it will not start. When you jump the starter it will sometimes clear the codes for ya to drive a few more days I replaced my whole transmission with one that had 60 k on it. Made it 9 months. Now I currently have the same exact problem again. These cars are cursed. (It's really a faulty design having the TCM inside a hot transmission) original trans had 130k on it before TCM acted out, two transmission services prior to TCM issues. This one now has about 69k on it, fully gone through when installed at 60k. And they're supposed to be vin locked and programmed so maybe you got lucky there, mine wouldn't start without being programmed when new tranny went in.

 

[LarryM]

Yes, gear indication light will disappear, limp mode, engine lights, ECT. You can get a thick wire, you'll need two people, you can jump your starter with the battery and wire (subwoofer size wire) but you need someone inside to push the start button when you do it at the same time, and it will start again. If the car doesn't know what gear it's in (TCM acting up) it will not start. When you jump the starter it will sometimes clear the codes for ya to drive a few more days I replaced my whole transmission with one that had 60 k on it. Made it 9 months. Now I currently have the same exact problem again. These cars are cursed. (It's really a faulty design having the TCM inside a hot transmission) original trans had 130k on it before TCM acted out, two transmission services prior to TCM issues. This one now has about 69k on it, fully gone through when installed at 60k. And they're supposed to be vin locked and programmed so maybe you got lucky there, mine wouldn't start without being programmed when new tranny went in.

Very interesting. That makes me nervous to replace the rest of the trans as I think it's more of a TCM or other electrical issue and not an actual mechanical problem with it. I do feel like it's possibly heat related, seems to happen more on hot days. Out of curiosity is yours an i-eloop car? That's definitely discouraging, would suck to do all the work to swap and then have problems again. I may just sell it and cut my losses if I can get it running good for a bit.

 

[LarryLondon]

Hi all, time to update this old thread!

It's been a year, and my problems mostly went away for a long period of time, and have continued to be nothing more than a pretty minor annoyance and the car operates just fine 98% of the time.. So I've just let it ride.

Two days ago I suddenly started having a new issue where there is a hesitation sometimes occurring after stopping at traffic lights or Stop signs. Again, still just a minor annoyance at this point but I decided to get it checked out again.

Took it to the transmission ship this morning, and the car is now displaying two codes that it was not before:

P2855 Low Clutch Hydraulic Circuit Failure
P2855 Low Clutch Piston Sealing Rings

They're saying the transmission should be replaced.

Just posting here because I don't know a lot and so I'm just asking if this sounds reasonable.

Thanks again.

 

[Lazy2.5]

Hi all, time to update this old thread!

It's been a year, and my problems mostly went away for a long period of time, and have continued to be nothing more than a pretty minor annoyance and the car operates just fine 98% of the time.. So I've just let it ride.

Two days ago I suddenly started having a new issue where there is a hesitation sometimes occurring after stopping at traffic lights or Stop signs. Again, still just a minor annoyance at this point but I decided to get it checked out again.

Took it to the transmission ship this morning, and the car is now displaying two codes that it was not before:

P2855 Low Clutch Hydraulic Circuit Failure
P2855 Low Clutch Piston Sealing Rings

They're saying the transmission should be replaced.

Just posting here because I don't know a lot and so I'm just asking if this sounds reasonable.

Thanks again.

No, it doesn't sound reasonable. Get a second opinion.

Take action before it gets worse.

 

[sinistriel@]

Hi all, time to update this old thread!

It's been a year, and my problems mostly went away for a long period of time, and have continued to be nothing more than a pretty minor annoyance and the car operates just fine 98% of the time.. So I've just let it ride.

Two days ago I suddenly started having a new issue where there is a hesitation sometimes occurring after stopping at traffic lights or Stop signs. Again, still just a minor annoyance at this point but I decided to get it checked out again.

Took it to the transmission ship this morning, and the car is now displaying two codes that it was not before:

P2855 Low Clutch Hydraulic Circuit Failure
P2855 Low Clutch Piston Sealing Rings

They're saying the transmission should be replaced.

Just posting here because I don't know a lot and so I'm just asking if this sounds reasonable.

Thanks again.

That is a very specific code. The TCM can detect through knowing how long the Low Clutch drum takes to fill vs the pressure switch tripping that the hydraulic circuit is leaking. Assuming the fluid is full, the ONLY way to repair that will be to start and disassemble the unit and begin testing the hydraulic circuit and see if it is leaking in the drum itself, if that is the case a new drum is needed because it is welded together and you can't replace the piston. Mazda has updated the drum design a few times since the units first came out and would be wise to install an updated one. There are sealing rings on the input shaft that can also leak. The Low Clutch is the input clutch for gears 1-4. If you were at a Mazda dealer the diag is very short, if the fluid is full then it needs a transmission.