Lost communication with transmission control module
Where to start
No communication with the transmission unit. The gearbox usually drops into limp mode and holds one gear. Power and earth first, then the connector — and only then the unit itself.
«No communication» is about the bus, not the unit
⛔ «No communication» almost never means «the unit is broken». It means one unit stopped hearing another, and the usual causes are power, ground and the bus — not the unit itself. Replacing a control unit on this code is the most expensive mistake in the whole reference.
Read the number of them. Several «no communication» codes at once point to something shared: power, ground, or a break in the bus. One code alone points to that unit's own connector and its power. Five missing units almost never mean five broken units.
⚠️ These codes also appear on their own after the battery has been disconnected, and clear themselves after a few trips. Clearing them without finding the cause is fine only in that case — otherwise they come back before you leave the yard.
How to put together a report a mechanic will actually read
How the code is built
All codes in «Communication between modules»
How the app helps
CarScan reads this code from your car through an OBD-II adapter, shows whether it is active now or only stored, names the module that reported it, and puts it into a plain-text report for your mechanic.