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All codes/U0101

U0101

Lost Communication with TCM

High severity

The ECU has stopped receiving messages from the transmission control module. The transmission falls into limp-home mode (typically locked in 3rd or 4th gear), the speedometer may stop working, and shift adaptation freezes.

The ECU has stopped receiving messages from the transmission control module. The transmission falls into limp-home mode (typically locked in 3rd or 4th gear), the speedometer may stop working, and shift adaptation freezes.

Common causes

  • TCM unpowered or grounded poorly

    One of the most commonly reported causes for this code — check this first.

    high

    Typical part cost: $60-2200

  • CAN wiring to TCM broken

    A plausible cause — test and verify before replacing parts.

    medium

    Typical part cost: $60-2200

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First things to check

  1. 1Confirm the code with a scan tool and check for additional related codes.
  2. 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.

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Tools you may need

Already have a compatible scanner? Use it. If not, a Bluetooth OBD2 adapter can help you confirm engine codes and check supported live sensor data before replacing parts.

Illustration of a Bluetooth OBD2 adapter, not a product photo

Basic checks

Veepeak OBDCheck BLE

A Bluetooth LE adapter for reading standard engine codes and supported live data.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Regular diagnostics

vgate iCar Pro BLE 4.0

A Bluetooth LE adapter with an automatic sleep feature for routine code and sensor checks.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Another option

OBDLink CX

A Bluetooth LE adapter to consider when comparing supported vehicles and diagnostic apps.

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Illustrations shown, not product photos. Check vehicle, phone and app compatibility before buying. These adapters do not guarantee access to ABS, airbags or manufacturer-specific systems. Clearing a code does not repair the fault and can reset emissions readiness monitors.

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Related codes

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Frequently asked questions

What does U0101 mean?

U0101 means "Lost Communication with TCM". It is a generic OBD-II code that points to a fault in the network / communication.

What are the most common causes of U0101?

tcm unpowered or grounded poorly; can wiring to tcm broken; gateway module routing can messages incorrectly — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.

Can I keep driving with this code?

This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly. Use the Wrenchify app for a full diagnosis specific to your vehicle.

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