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That certainly seems like about as good a price as you'll find for a non-salvage yard TCM.

Do you still have the TCM out right now? If so, and you can find pin location AC on the TCM connector, it will be very simple to run the final electrical test that I mentioned previously. Just set your meter to Ohms (resistance), and probe the leads from TCM AC to speed sensor B. It should read around 1-2 Ohms.
 

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Discussion Starter #43
I do have the TCM on my desk right now, but I may not be understanding how to perform this test. Assume battery connected and finding AC on the TCM plug?

105484
 

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This is a resistance test, so the battery does not need to be connected.

On the picture that you posted of the TCM connector, at the upper left there are 2 pin slots missing on the top row. Past that gap, count over 3 pin slots - that third actual pin slot is AC. Now set your meter to Ohms (or the lowest Ohms setting if there is more than 1 setting). Take one meter lead and probe the middle (red wire) pin slot of the speed sensor connector. The other meter lead will be used to probe AC of the TCM connector. If the meter lead doesn't want to make contact at the TCM connector, just take a paper clip or piece of thin, solid wire and use that as a bridge to connect the lead. The reading should be around 1-2 ohms (or maybe perhaps even zero). If you see the letters OL, then something is not making contact.
 

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Damn, you have an E TCM. That's the latest (I think). If you don't have to turn it in for a core, I'll take it off your hands should you end up replacing it.
 

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Discussion Starter #47 (Edited)
Summary to date:

I have everything taken apart with TCM in hand.

Testing the speed sensor plug seems to be fine, although slightly low in volts.

Checked the TCM fuse on the panel and the 15 amp fuse looks fine.

I have used an electrical cleaner on the various sensor connections, which seemed to improve electrical flow but going to assume didn't fix the underlying problem.

Seems my only option now is to replace this TCM, which is a gamble because I can't test the TCM to verify it is in fact the problem.

Going to be really disappointed if I do replace the TCM, put it all back together, and end up with the same CEL and code.


Kind of feel like cleaning all the plug connections with electrical cleaner, putting everything back together, going for a ride, and just confirm I do in fact still get the code. If code comes back, then yes to TCM replacement.
 

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Discussion Starter #48
Also looking at the Mazda Parts site, it does say LF8M-18-9E1H replaces LF8M-18-9E1G. I wonder what changed going from G to H and if it's worth swapping my G for an H version.

105486
 

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… Kind of feel like cleaning all the plug connections with electrical cleaner, putting everything back together, going for a ride, and just confirm I do in fact still get the code. If code comes back, then yes to TCM replacement.
If you can live with the extra work, that would be a really good thing to try.

Were you able to try the resistance test from the speed sensor signal wire to AC on the TCM connector?
 

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Discussion Starter #50
I set my multimeter to the pic below, put a needle in the 3rd slot over from the 2 empty slots, connected the black plug to the inserted needle, connected the red plug to the middle (red) on the speed sensor cable, and got a reading of 0.1 on the meter.

Not 100% sure I performed that test correctly.

105487
 

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…. Not 100% sure I performed that test correctly.
Your testing was fine, with a result of somewhere around 20 Ohms. The meter doesn't have fine resistance resolution on the low end, but no big deal because it's probably close enough in this case.

If you're going to put it back together and try it again, then first scrub the pins on the TCM with electrical cleaner and a small brush, and make sure that AC pin is completely clean. And also reconnect the TCM connector into the TCM a few times, which might dislodge any corrosion that might be deposited inside the female slots of the connector. A bit of electrical cleaner on the pins might help on that as well.
 

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Discussion Starter #52 (Edited)
If you can live with the extra work, that would be a really good thing to try.

Were you able to try the resistance test from the speed sensor signal wire to AC on the TCM connector?
Well, I buttoned everything back up and took it for a ride. It did take longer for the CEL and AT lights to come one. This time however, there is an additional new code 'U0101 - lost communication with TCM'. Not sure what I did that resulted in this code, but I guess this leans more toward a bad TCM?

Also, as before the 'AT' light does come on the dash, but doesn't stay on for long.

The car drives and shifts fine by the way. It also allows me to go into manual mode when the AT light goes out.

edit: I didn't scrub the pins....
 

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…. there is an additional new code 'U0101 - lost communication with TCM'. Not sure what I did that resulted in this code, but I guess this leans more toward a bad TCM?
….
That code is interesting in a couple of ways. If the TCM was consistently no longer able to communicate, it should go into limp mode with very limited shifting, so I think it was probably just a momentary, transient loss of communications.

And the other curious thing about that code is that one of the 2 CAN (communications) pin slots in your TCM connector picture is quite discolored (the one all the way to the right in the middle row). I don't know if that discoloration is in any way related to what's going on electrically, but it would be somewhat of a coincidence if it's not.

It's unfortunate you weren't able to clean the TCM pins and connector, because that would have closed the book on everything that you can possibly do, other than hanging on a replacement TCM. Again, I can't tell you that cleaning would eliminate the codes, only that it's a bit disappointing to have a loose end hanging around. But I'm sure you have had WAY more than enough of taking this apart a putting it back together again.
 

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Discussion Starter #54
That code is interesting in a couple of ways. If the TCM was consistently no longer able to communicate, it should go into limp mode with very limited shifting, so I think it was probably just a momentary, transient loss of communications.

And the other curious thing about that code is that one of the 2 CAN (communications) pin slots in your TCM connector picture is quite discolored (the one all the way to the right in the middle row). I don't know if that discoloration is in any way related to what's going on electrically, but it would be somewhat of a coincidence if it's not.

It's unfortunate you weren't able to clean the TCM pins and connector, because that would have closed the book on everything that you can possibly do, other than hanging on a replacement TCM. Again, I can't tell you that cleaning would eliminate the codes, only that it's a bit disappointing to have a loose end hanging around. But I'm sure you have had WAY more than enough of taking this apart a putting it back together again.
Well at this point, it takes me like 5 mins or less to take off things to get to the TCM. I will do that just to clean the male pins on the TCM as well as the female pins on the TCM plug because I do have the time.
 

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Hats off to you for giving a 100% effort on this, regardless of how it turns out! We know these things don't always go our way, but you have certainly done enough to deserve victory on this one, and perhaps the automobile gods will eventually give you the win.
 

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Discussion Starter #56
Hats off to you for giving a 100% effort on this, regardless of how it turns out! We know these things don't always go our way, but you have certainly done enough to deserve victory on this one, and perhaps the automobile gods will eventually give you the win.
I did clean the both sides of the TCM. When plugging it back in, I can't get the white bar here to actually lock into place.

105488
 

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Well, I buttoned everything back up and took it for a ride. It did take longer for the CEL and AT lights to come one. This time however, there is an additional new code 'U0101 - lost communication with TCM'. Not sure what I did that resulted in this code, but I guess this leans more toward a bad TCM?

Also, as before the 'AT' light does come on the dash, but doesn't stay on for long.

The car drives and shifts fine by the way. It also allows me to go into manual mode when the AT light goes out.

edit: I didn't scrub the pins....
That's a bad TCM. Happened to my car except in addition to the AT light, the whole dash lit up like a Christmas tree and there was a pronounced SLAM at the floorboards. It was as if I'd struck something. I was driving at 75mph at the time and it scared the shit out of me. I babied the car on back roads to get home, and the SLAM continued no matter what. The transmission shop pulled that code when I brought it in. Once the TCM was replaced, no problems.

It's possible the seating and removing of the connection could have broken some corrosion away; however, since the TCM is mounted directly to the transmission, there are theories out there that the massive amount of heat from the transmission is what does them in. I've seen instance where people rig up some kind of heat shield for the TCM.

Use yours as a core to send to a rebuilder in exchange for another. If you don't go that route, I would take it off your hands.
 
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