Threw a U0101 code: Lost Communication With Transmission Control Module (2010 Mazda3)

[dsims]

The car (2010 Mazda 3, 2L, with 91K miles) threw a U0101 code: Lost Communication With Transmission Control Module. The code was not permanent, and I was able to erase it with an OBD tool. I noticed that the battery was 6 years old, so I replaced the battery. Afterwards, the code was thrown again, this time permanent. Also the AT and DSC lights came on. The car would also lose throttle control. The engine ran, but pressing on the accelerator did not increase the RPMs.

I reset the ECU by disconnecting the battery cables and touching them together for 5 minutes, which is what is recommended to drain any capacitors that might be holding a memory for the ECU. Afterwards, all seems OK. I drove the car for 1.5 hours today, including highway driving, and no lights, no throttle issues.

I'm thinking that if you need to replace the battery to fix electrical problems you have to take the next step and reset the ECU.

 

[dsims]

Scratch the above. After driving the car for about 2 hours the CEL came back on with the same code:

U0101 code: Lost Communication With Transmission Control Module.

 

[dsims]

I removed the Transmission Control Module and sent it to UpFix. They fixed it for about $275. After I reinstalled the TCM no codes have been thrown after 10 days of driving. If you have the same year car, it's easiest to get at the TCM's screws by removing the bracket with the motor mount that is covering one of the TCM's screws.

 

[Mickeye5]

The car (2010 Mazda 3, 2L, with 91K miles) threw a U0101 code: Lost Communication With Transmission Control Module. The code was not permanent, and I was able to erase it with an OBD tool. I noticed that the battery was 6 years old, so I replaced the battery. Afterwards, the code was thrown again, this time permanent. Also the AT and DSC lights came on. The car would also lose throttle control. The engine ran, but pressing on the accelerator did not increase the RPMs.

I reset the ECU by disconnecting the battery cables and touching them together for 5 minutes, which is what is recommended to drain any capacitors that might be holding a memory for the ECU. Afterwards, all seems OK. I drove the car for 1.5 hours today, including highway driving, and no lights, no throttle issues.

I'm thinking that if you need to replace the battery to fix electrical problems you have to take the next step and reset the ECU.

Dude on new cars you're lucky you didn't cry your main computer by touching the battery cables directly together. That's old school and understand. You need to get a 10 amp capacitor, and put it between the cables if you do another reset. Believe me it's a lot safer..

 

[Gozo]

You mean a 10 ohm resistor, right? Capacitors aren’t rated in amps.
Probably could just hit the brakes and the brake lights would drain any residual charge down.

 

[Mickeye5]

My bad. Resistor yes.