The transmission control module in my 2007 Mazda 3 is playing up, I was wondering if I can just replace it with another one from a Mazda the same year and make. I've been told it has to be coded in to the gearbox, and I'm not sure what to do. I've seen videos on the internet where people have just swapped them out.
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. The good news is that there are companies out there who can repair your existing TCM, which gets you around the need to buy an expensive replacement. By the way, from what I can gather, any replacement TCM should be plug-and-play with no need to have the new module coded to the car’s other systems.
It’s also worth noting that Mazda in the USA issued a Technical Service Bulletin (like a recall but not for a safety issue) for automatic 3s from this era fitted with the 2.3-litre engine. In some cases, the shift solenoid could lose fluid, leading to harsh shifts and shuddering when driving uphill. The fix was a revised solenoid design but the catch was that the unit lived inside the transmission, so to whole gearbox had to be removed and taken apart to replace the part in question.