U0101 - LOST COMMUNICATION WITH TRANSMISSION CONTROL MODULE (TCM)

The U0101 OBDII fault code is a generic code in most brands and models of vehicles. It indicates that the TCM (Transmission Control Module) has no communication with other vehicle control modules.

Usually, the Control Area Network (CAN) is the most used circuit for the communication of these modules. Without this network, it is not possible to carry out the information exchange that the modules perform, nor is it possible for a scanner to get information from the vehicle.

• Check Engine light illumination.
• Gear changes are not possible.
• Vehicle stalls in 2nd or 3rd gear.

Reasons why the U0101 OBD2 diagnostic code is set:

• The - or + circuit of the Control Area Network may be open.
• The CAN bus power circuit or CAN bus ground circuit may be shorted.
• The Transmission Control Module may be defective.

The steps to troubleshoot the DTC U0101 OBDII code are the following:

• To start the diagnosis, consult the TSB (Technical Service Bulletins).
• Check if other fault codes are stored, especially if they are related to bus communication or the battery. If so, diagnose those codes first.
• Check that the fuses that turn on the TCM are in good condition and that the ground connections are tightened correctly. Make any applicable corrections and clear the code.
• If the code returns, locate the CAN bus communication connections and make a wiring inspection. If they are damaged due to high temperatures or rubbing, repair or replace them.
• With a DVOM, check the TCM has proper power and ground signal. Follow the manufacturer's steps for such a diagnosis. If you determine that the TCM is defective, go to a specialized service center.