U0101 fault code: what it means

U0101: Lost communication with the transmission control module (TCM). Gearbox may be stuck in limp mode.

Network (communication between modules) · Costly if missed

Usual causes, most likely first

TCM power, fuse or earth fault
damaged CAN wiring or connector
faulty TCM
low battery voltage

U0101 by make

Ford

Lost communication with the transmission control module. On Ranger usually a power or earth problem rather than a dead module.

Usual causes: weak battery or voltage drop; bad earth or wiring; TCM failure

Haval

Lost communication with the transmission control unit. Gearbox warning and possible limp mode.

Usual causes: low battery voltage; TCU connector or CAN wiring; faulty TCU

Land Rover

Lost communication with the transmission control module. On Discovery 4 can cause gearbox fault message, limp mode or no start.

Usual causes: failed TCM or valve body/mechatronic unit; low battery voltage; water in TCM/gearbox connector; CAN wiring fault

Mercedes-Benz

Lost communication with the transmission control module (TCM).

Usual causes: TCM / conductor plate fault; wiring or connector fault; low battery voltage

MG

Lost communication with the transmission control unit.

Usual causes: low battery voltage; TCU connector or CAN wiring; faulty TCU

Subaru

Lost communication with the transmission computer (TCM).

Usual causes: weak or failing 12V battery; CAN wiring or TCM connector fault; TCM power supply fault

What the repair usually costs

Automatic transmission rebuild, 6-speed and up (sent to specialist)NZ$7,190–NZ$13,080 · A$6,190–A$11,830
DSG / dual-clutch mechatronic unit replacement (new or reman)NZ$4,300–NZ$7,160 · A$3,750–A$6,390
DSG mechatronic repair / rebuild (unit sent to specialist)NZ$2,070–NZ$4,800 · A$1,890–A$4,250
12 V battery replace, standard flooded (small / medium car)NZ$190–NZ$330 · A$170–A$310

Not sure what U0101 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.