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Discussion Starter · #1 ·
We just purchased 2008 3 with 175k on it from the original owners.

The car is in like new condition both inside and out, and has all the service records from new.

The owners went to the store and when they were leaving the car made a noise and they thought the trans was slipping.

They called the local shop that they use and were told over the phone that it needed a trans without the shop looking at the car. They went and purchased another car.

We bought it for $500, I figured that it was is such good condition that It was a good value even if it need repair.

I trailered it home and put my scanner and it read "'Lost communication with TCM''. I had not driven the car at all and there was no AT light on

So after looking on the forum I sent off for a TCM from UpFix.

Received the part and put it in, took it out to give it a test never went over 25mph.

Went about 100 yards and the check engine light and the AT light came on.

Brought it back hooked up the scanner and NO codes just the AT light on.

Any Ideas?

Thanks in advance.
 

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Discussion Starter · #3 ·
Wires to the TCM look good no frayed or chewed on wires.

The scanner shows no codes but the Check engine light is on.

I will check fuse #27.
Thanks
 

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Definitely check wiring, which isn't that easy as it is wrapped. I went thru this 9 months or so back. Keep in mind all TCM's are not repairable, the guy that fixed mine, well actually did not fix, refunded me the cost, which I used to buy a brand new one. The new one did the trick, could tell as soon as it started, its been fine now. If it comes to this, you can get a decent deal online from some Mazda dealers.
 

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Discussion Starter · #5 ·
Thanks.

I must be lame I do not see a wiring diagram in the service manual.

Where is the AT relay located?

The service manual says to:
On-Vehicle Inspection

1. Inspect the power supply circuit for the VSS.
a. Remove the insulator from the transaxle.


b. Disconnect the VSS connector.


c. Switch the ignition to ON (engine off).
d. Measure the voltage at VSS connector terminal A (harness-side).


  • If there is any malfunction, repair wiring harness between VSS and AT main relay.
  • VSS specification

  • B+
e. Switch the ignition to off.
f. Connect the VSS connector.
2. Inspect the GND circuit for the VSS.
a. Switch the ignition to off.
b. Measure the voltage at VSS connector terminal C (harness-side).


  • If there is any malfunction, repair wiring harness between VSS and GND.
  • VSS specification

  • Below 1.0 V
3. Inspect the signal circuit for the VSS.
a. Connect the oscilloscope to the following TCM connector terminals and set it as below.
  • (+) lead: TCM terminal Z
  • (-) lead: battery negative terminal
  • Oscilloscope setting: 1 V/DIV (Y), 2 ms/DIV (X), DC range
b. Start the engine.
c. Measure the wave form when the following conditions are met.
  • Gear position: 3GR
  • Vehicle speed: 30 km/h {19 mph}


  • If there is any malfunction, replace the VSS..
 

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You state check engine light is on but no codes. What are you using to scan this car with, I used Torque Pro on an Android and it picked up the codes. There are probably better readers out there, but Torque Pro has worked well for me over the years. Maybe try another code reader?
 

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Discussion Starter · #7 ·
I checked fuse 27, looked fine I did hit legs with a bit of sandpaper to make sure that there was good contact.

Plugged in the scanner and hit the clear code even though there was no code. CEL went out.

I will give it a test drive.
 

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You stated this above, Lost communication with TCM. This does not sound like a trans rebuild to me, but be careful you can spend a couple of grand on a trans rebuild and still have a non-fuctioning transmission if the TCM doesn't work (or there is some other issue). I admit there is a lot of miles on the trans, but if maintained they go a long time, got the same trans in a 6 with 200k miles on it and it is fine. Good luck.
 
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