Error 12C will not disappear

We keep getting an error 12C for motors. Ports 1 and 6 are fine, but when we plug it into any other port we get the error message. We changed cables several times. Our connections are fine. We changed motors, brain, controllers. We callibrated the motors and updated firmware about 20 times. In addition, we have lost Help! We are at a loss. Eli sent us youtube links for calibrating and updating firmware and followed instructions to switch out cables. Now what can we do?

Hi Linda,

We’re sorry that you are having this problem. To help resolve this problem, we have a few questions:

Are these I2C errors occurring with the built-in programs such as Driver Control or Autopilot, or are they occurring with a custom Modkit or ROBOTC program? Is the Robot Brain confirmed to be running the latest firmware (v1.12 or newer for the Robot Brain)? Some older versus of the Robot Brain firmware had intermittent bugs that could cause I2C errors; these are corrected in the most recent firmware.

Do the I2C errors occur while the Robot is moving or completely stationary (nothing is moving)? If the I2C errors occur while the Robot is moving, then the most likely cause is from the Smart Cables having an intermittent connection, and the most likely cause of this issue is that the cables are not fully plugged in. A loose connection here can cause the I2C error. Please test all of the Smart Cables by pressing them in until you hear an audible click sound from the latch.

If the Smart Cables appear to have a secure connection, then the I2C error can also be caused by internal damage to the Smart Cable. This can be caused by pulling very hard on a Smart Cable to remove it while not pressing on the release latch or if the cable was tied into a knot. To see if this is the cause, please use a single Motor/sensor on the same port of the Robot Brain, then swap cables one at a time. Does the problem follow a specific cable? If no issues were seen, use a different Motor/sensor on a different port, and try swapping cables again. Is there a pattern where a specific cable, port, motor/sensor, or Robot Brain causes the I2C errors?

If you are still having issues, or if you have identified that a specific cable or motor/sensor is causing the I2C errors, then please contact our Technical Support team at or by calling +1-903-453-0802 so we can resolve the situation.


  • Art

I saw in another thread to do the VEX IQ firmware update, but to unplug all the motors and just test one in port one. After this, I was able to fix the motor and no longer get the 12C error. That should fix your problem.

I too have had problems with the IC2 Errors on a few motors. I I did everything that Linda did above and no luck. I swapped out cables, replugged in cables, updated Firmware and I still have a few motors (2) out of 20 kits that do not work. I am sending them back to Eli for him to look at. This was with RobotC for my students. The motors start moving and then crash and stop. Once they stop they do not restart. I had one motor get very hot when students had it in a clawbot and were trying to use the claw with the bad motor

Have experienced this issue and have tried everything mentioned above. It was a brand new motor used approx 20 mins total over several weeks. Have also tried plugging this on a second brain. The I2C error does not go away. Each time we change the port on this motor, the error appears on that port, which finally is just the motor gone bad probably. Our older motors from last year were still working fine.

Hi surgeon,

We’re sorry that you have encountered this issue. If you have a new Smart Motor that has an I2C error on every port on your Robot Brain, then please contact our technical support folks at or by calling +1-903-453-0802 so we can replace this motor.


  • Art

Thanks Art. Will do.

If we are not using any kind of programming yet, do we still need to update all the motors and brains?

HI Deborah,

The firmware updates are not normally required, but highly recommended for everyone as they contain bug fixes and/or new features.

There are two main reasons that would require updating the firmware:

  1. To make use of new features and/or bug fixes in Modkit for VEX or ROBOTC custom programs

  2. A Smart Motor, Controller or a new sensor was purchased and the firmware that is included in it is newer than your Robot Brain’s version.

Both of these can be resolved by updating the firmware on all devices:


  • Art