I have a pololu dual mc33926 motor driver shield sitting on top of an arduino mega 2560 driving 2 maxon 363789 motors. The arduino is powered by usb serial and the motor driver is powered by lityum ion battery pack. This works fine on one side of my robot. Additionally the other side has exactly the same setup to drive 2 other maxon motors. However for some reason when power is given to both the driver and arduino on that side , motor1 constantly and at full speed turns. I replaced the arduino with a new one and also the driver with a new one but the problem persists. The shields motor1 led is constantly green. I also uploaded an empty code into the arduino and with power given the motor still constantly turns. (Note: the side that has this problem; there is a nrf24l01 connected to the arduino) when uploading a code that publishes ros topics, the topics are published without problem. This doesnt look like a code problem as the motor still turns with empty code. To verify the motor1 problem i swapped the two motor's cables therefore the other motor connected to motor1 port of the motor driver is now turning.