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ElectricalSeverity High: diagnose before driving on

U0101Lost Communication With TCM

What it means

A control module stopped receiving messages from the transmission control module on the data bus (CAN). The transmission control module may be without power or ground, or the bus wiring to it is faulty.

Symptoms

  • Transmission in limp mode
  • Several warning lights at once
  • Other modules may store related codes

Common causes

  • No power or ground at the transmission control module
  • CAN wiring open, shorted or corroded (CAN-H / CAN-L)
  • Low battery voltage during cranking
  • Failed transmission control module

What to check first

  1. Check fuses, supplies and grounds at the transmission control module
  2. Measure CAN-H to CAN-L resistance with the battery disconnected (about 60 Ω on most cars)
  3. Scope CAN-H and CAN-L for a clean mirrored signal
Can I drive with U0101? Not recommended. U0101 can lead to stalling, limp mode or engine damage; diagnose it before driving further.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

How to test the parts behind U0101

CAN bus networkWiring, typical values, multimeter and scope tests

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U0101: questions and answers

What does U0101 mean?

U0101: Lost Communication With TCM. A control module stopped receiving messages from the transmission control module on the data bus (CAN). The transmission control module may be without power or ground, or the bus wiring to it is faulty.

What are the symptoms of U0101?

Transmission in limp mode. Several warning lights at once. Other modules may store related codes.

What causes U0101?

No power or ground at the transmission control module. CAN wiring open, shorted or corroded (CAN-H / CAN-L). Low battery voltage during cranking. Failed transmission control module.

How do you diagnose U0101?

1. Check fuses, supplies and grounds at the transmission control module 2. Measure CAN-H to CAN-L resistance with the battery disconnected (about 60 Ω on most cars) 3. Scope CAN-H and CAN-L for a clean mirrored signal

Can I drive with U0101?

Not recommended. U0101 can lead to stalling, limp mode or engine damage; diagnose it before driving further.