Robot light slowly flashes red on cortex only when using field controller

Our robot light on the cortex randomly slowly flashes red whenever we use the competition switch in EasyC v4 to test our autonomous.

We used fully charged batteries (on safe) in both the controller and the cortex and we are still experiencing this problem.

We switched out the new cortex for the older model, re-linked vexnet keys, downloaded latest firmware on BOTH joystick and cortex (V3.17) and still have this problem.

The robot runs fine without interruption when we’re not using the built in competition switch, however.

We also checked our batteries with a voltmeter and they seem to be fully charged whenever we use them (~8V).

Any suggestions?

According to the Cortex manual, a Slow Red robot blink means a User Microprocessor issue. Have you updated your Cortex? If both your Cortex and your Joystick are up-to-date, you may want to contact VEX Support at

They’re up to date to the Firmware version before today’s update.

This sounds like a similar issue as in this thread: (though I could be wrong)

Some things to try:

  1. Use different VEXnet keys
  2. Tether the Joystick and Cortex with the USB A-A cable
  3. Use a different Joystick
  4. Use an older version of EasyC (with an older version of the VEXnet firmware (Master Code))

If 4 fixes it, then you may have the same problem as in the thread above.