Transmission Control Module (TCM) faults are not unknown on these early Mazda 3s. Symptoms usually involve erratic shifting, a failure to select gear at all and having the car go into limp-home mode.

This input ensures the transmission control module engages the proper gear ratios smoothly based on rpm data and throttle position. Sensor data helps optimize shift timing, pressures, and lockup ...

To convince the transmission control module that a working automatic was still installed and clear the fourteen-odd diagnostic codes, [Dean] put together a block of eight common automotive relays.