TCU (Transmission Control Unit)

The manual gearbox is on its way out. Modern automatics are fast, they can lower the fuel consumption by changing the settings and they are easy to control. Speaking about control: the modern automatic gearbox always uses a dedicated computer, the transmission control unit. As long as it’s working, it’s a great piece of engineering. However, when it fails…

What if the TCU fails?

Exactly, what happens if the TCU fails? Luckily most transmission control units have some sort of limp mode, so you can still drive home or to the nearest garage. There will be a failure warning visible in the instrument cluster though. Also, not all gears will be available while driving in limp mode. Automatic gearboxes are complicated devices so take your car to a real specialist once a problem occurs.

What does it cost to remanufacture a TCU?

You should keep in mind that removing and replacing a TCU can be a tough job, so there will be additional costs. But, it’s still lucrative to remanufacture a TCU, since a new part will be hugely expensive. We don’t recommend trying a used part, because they often have the same weaknesses and will also fail eventually. And if that’s the case, you’ll have all those costs all over again.

What company should I choose for the repair / remanufacturing of a transmission control unit?

Opt for a specialist, like a dedicated gearbox repair specialist or companies like BBA Reman and ACtronics. This isn’t a job for hobbyists.

Useful sources:

https://en.wikipedia.org/wiki/Transmission_control_unit

http://ken-gilbert.com/wrx/STi_Manual/08.%20MECHANISM%20AND%20FUNCTION/33.%20AUTOMATIC%20TRANSMISSION/13.%20Transmission%20Control%20Module%20(TCM).pdf