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Mazda TCM Troubleshooting

Eminent Member Moderator

If you're still having issues with your TCM after it has been refurbished. Here are some general tips to help you further troubleshoot the issue:

  • First, check that the vehicle's car battery is fully charged and getting a good connection.
  • Check the TCM fuse.
  • Inspect the pins on both the harness plug as well as the TCM and make sure the pins are not pushed back on the harness plug. If some of the tabs are broken on the TCM plug the harness will have to be manually pushed in further towards the TCM to ensure a good connection.
  • Clean the pins with electronic cleaner on both the harness plug as well as the TCM itself and inspect for any dirty or receding pins.
  • Check the transmission fluid. If it's very dark and the filter is full of debris, it'll show trouble codes and the A/T along with the check engine light might come on. This is highly likely if the transmission fluid was never serviced and the vehicle has over 75,000 miles. 


Perform a hard battery reset with the TCM plugged back into the vehicle to clear any remaining codes and reset the TCM:

  • Remove the key from the ignition.
  • With the battery removed, to ensure there is no power, short the battery cables in the vehicle and connect the positive and negative cables together for at least 20-30 minutes.
  • Reconnect the battery cables starting with the positive cable on the battery first.

This will reboot all the computer modules including the TCM and make the vehicle relearn its own values.

It's recommended to have the vehicle idle for a few minutes then take it for a drive at least 15-20 minutes after the hard battery reset. 

It might idle rough at first and shift strangely but it should smooth out after the drive. 

If you're not confident in doing the hard battery reset, simply leave the car battery disconnected overnight. The main goal is to drain the voltage in the computer modules to reboot them. 


Troubleshoot 'No Communication' by using a multimeter, and check that there is continuity between the battery and the pins on the harness plugs. Testing the wiring harness pins for any connectivity issues:


Mazda 3 TCM Connector Troubleshooting clipped rev 1


Refer to the image above for the pinout of the Mazda TCM Wiring Harness 

  • Power: I, O (Red)
  • Ground: X (Black)
  • Can-Hi: B (Orange)
  • Can-Lo: E (Blue)


There should be continuity between the positive post on the battery and the red pins (I & O).

There should be continuity between the negative post on the battery and the black pin (X). 

For any communication issues, with the ignition-on, make sure that you do an ohm test between Pin B (Orange) & Pin E (Blue) on the harness plug for any remaining U0100 and U0101 (no communication) issues that are still present after the repair. There should be 120-ohm resistance. 

If there is no ohm resistance present when you test between pins B & E then the issue is not the TCM. Check the pins and wiring all the way to the OBDII connector pinout.

Check the wiring harness for any pinched or torn wiring, check & clean the connector pins on the harness plug, and inspect closely with a flashlight for any corrosion or receding pins.

Pin B on the TCM plug should have continuity to Pin 6 on the OBDII connector under the dash driver-side. Pin E on the TCM plug should have continuity to Pin 14 on the OBDII connector. 

OBD2 Connector Pinout

P0715 - Input Turbine Speed Sensor Malfunction

If you are having this code show up on the OBDII scan tool then it's most likely a defective speed sensor that needs to be replaced. 

The speed sensors on the Mazda 3 and Mazda 5 are actually commonly known to fail and are relatively inexpensive to replace. 

P0753 - Shift Solenoid 'A' Malfunction
P0762 - Shift Solenoid 'B' Malfunction
P2709 - Shift Solenoid 'F' Malfunction

If this code is still present and won't clear after the TCM has been refurbished, please make sure to check the transmission fluid and filter. If the fluid is dirty and the filter is clogged up these codes might not clear. 

Once the transmission fluid and filter have been inspected/serviced the code should clear with an OBDII scan tool. If not, it may be a defective Shift Solenoid A (P0753), B (P0762), or F (P2709) that needs to be replaced. 

P0732, P0733, P0744 DTCs

If you have one or more of these codes even after your transmission computer module has been refurbished. Please check the fluids and filter of your transmission. If the vehicle already has more than 130k miles and the fluids haven't been replaced yet there may be already physical problems with the transmission not just the TCM. 



This topic was modified 1 year ago 4 times by Ernest
This topic was modified 11 months ago by Ernest
This topic was modified 3 months ago by Ernest
Topic starter Posted : 04/18/2022 10:32 pm
New Member Registered

I had received the TCM part and installed. But the "AT" light on is still. There is a "M"(manual) light instead of "D"(drive) when transmission switch put on "D' slot. Also manual switch does not work at all!


Posted : 06/28/2022 1:03 am
Eminent Member Moderator

What codes are you getting? Please reach out to our customer service so we can assist you further. 

Topic starter Posted : 06/29/2022 1:02 am
Serge - UpFix Team
Famed Member Moderator

I apologize you're still having issues with your part!  Could be that you have an active code. Please have your part scanned for codes and let Customer Support know what codes you are getting so they can create a support ticket and have a technician reach out. Make sure you have your order number ready when you call. 1-888-979-9343

Posted : 06/29/2022 1:05 am
New Member Registered

I went to AutoZone and the report comes out the code is P0745-00 (PCA) and U0101-00.

Posted : 06/29/2022 1:12 am
Serge - UpFix Team
Famed Member Moderator

Check or Repair damaged wiring or connectors.

Check or Repair ground connections.

Call costumer service if you still have issues.  Have your order number ready and codes.  They will create a support ticket 

Posted : 06/29/2022 11:48 pm
Bryan Caldwell
New Member Registered

2010 Mazda 3. Refurbished TCM just installed. Car will not turn over, just keeps cranking. Battery is strong.

Wiring harness attaches firmly. Battery then disconnected for 30 minutes. 15A TCM fuse is good. Any suggestions? 

Posted : 12/02/2023 9:07 pm
Serge - UpFix Team
Famed Member Moderator

What codes are you getting? If your car dont start it could be many other issues like bad starter or spark or even fuel pump . Scan for codes and post them here.

This post was modified 8 months ago 2 times by Serge - UpFix Team
Posted : 12/02/2023 10:47 pm
Jose Garcia
New Member Registered

Order: 811589H      Web:100382528 

I’m still getting the following error codes after installing the repaired TCM/TCU:  

P0732-FF Transmission gear #2 - incorrect ratio

P0733-FF Transmission gear #3 - incorrect ratio

P0734-FF Transmission gear #4 - incorrect ratio

P0744-FF TCC ( control circuit high)

U1900-A0   (CAN) Communication bus fault- receive error


Is it safe to do a whole transmission flush?…. I’m looking to do a transmission flush, change transmission filter and gasket to see if that fixes the issue.


Posted : 04/23/2024 11:44 pm
Serge - UpFix Team
Famed Member Moderator

Looks like a mechanic had your vehicle with those exact codes. If those codes show up together it's possible that the transmission itself is faulty. It's not something you would like to hear but it's a possibility.  You can check transmission fluid and filter and see how dark it is and if there is metal debris.  However, the U1900 - if this code shows up while scanning the TCM for codes, it's possible that the TCM or the wiring is at fault. Since it's only been in here once, I'd recommend checking fluids, and filter,  if needed, we can take another look under warranty at the TCM before blaming the transmission for going bad

This post was modified 3 months ago 4 times by Serge - UpFix Team
Posted : 04/26/2024 1:52 pm