TCM

📖 YOUCANIC Automotive Glossary

The TCM (Transmission Control Module) is the dedicated computer managing automatic transmission operation — controlling shift timing, shift quality (clutch apply pressure and overlap), torque converter lockup, line pressure, and in some cases transfer case and all-wheel-drive functions. The TCM receives inputs from transmission speed sensors (input and output shaft), fluid temperature sensor, range sensor (gear selector position), and brake switch, while also reading engine data from the ECU via CAN Bus to coordinate shifts with engine torque.

TCM failures cause transmission warning lights, harsh or delayed shifts, stuck in one gear (limp mode), no-shift conditions, and torque converter shudder. DTCs: P0700 (Transmission Control System Malfunction — a flag code indicating TCM has stored its own codes), P0715-P0720 (speed sensor codes), P0750-P0770 (shift solenoid codes). The YOUCANIC UCAN-II reads TCM codes separately from engine codes — always check TCM codes when experiencing shift problems, as they are not visible through basic OBD2 code reading.